the phrase “ sensorineural hearing loss ” refers to hearing loss caused by loss of neurons . such hearing loss can be , for example , genetic in origin . another example of sensorineural hearing loss is antibiotic - induced , such as aminoglycoside - induced , hearing loss . sensorineural hearing loss can also be induced by excessive sound . “ neurotoxin poisoning ” refers to poisoning caused by a neurotoxin . a neurotoxin is any chemical or substance that can cause neural death and thus neurological damage . an example of a neurotoxin is alcohol , which , when abused by a pregnant female , can result in alcohol poisoning and neurological damage known as fetal alcohol syndrome in a newborn . other examples of neurotoxins include , but are not limited to , kainic acid , domoic acid , and acromelic acid ; certain pesticides , such as ddt ; certain insecticides , such as organophosphates ; volatile organic solvents such as hexacarbons ( e . g . toluene ); heavy metals ( e . g . lead , mercury , arsenic , and phosphorous ); aluminum ; certain chemicals used as weapons , such as agent orange and nerve gas ; and neurotoxic antineoplastic agents . “ neurodegeneration of the visual pathway ” refers to neural cell death occurring in neurons involved in vision , for example neurons in the occipital lobe , optic nerve , and retina . neurodegeneration of the visual pathway can be caused , for example , by a stroke in the visual pathway , for example a retinal stroke . stoke can also occur in the optic nerve or the occipital lobe . neurodegeneration of the visual pathway can also be caused by neurodegenerative diseases , for example macular degeneration . neurodegeneration of the visual pathway can also be caused by diseases that are not necessarily considered neurodegenerative , such as glaucoma , which can cause retinal degeneration . “ non - vascular headache ” generally refers to headaches other than migraines . examples of non - vascular headaches include , but are not limited to , stress headaches and sinus headaches . the terms “ treatment ”, “ treating ”, and the like , refer to reversing , alleviating , or inhibiting the progress of the disease or condition to which such term applies , or one or more symptoms of such disease or condition . as used herein , these terms also encompass , depending on the condition of the patient , preventing the onset of a disease or condition , or of symptoms associated with a disease or condition . such prevention also includes reducing the severity of a disease or condition or symptoms associated therewith prior to affliction with said disease or condition . thus , “ treatment ” encompasses administration of the antagonist to a subject that is not at the time of administration afflicted with the disease or condition , and “ treatment ” can include preventing the recurrence of a disease or condition or of symptoms associated therewith . conditions wherein a patient who is not at the time of examination afflicted with a disease or condition but could benefit from treatment according to a method described herein can be recognized by a healthcare professional , such as a medical doctor , of ordinary skill . nr2b subunit selective nmda antagonists that can be used in the methods of the present invention include compounds of formula i ( a ) r 2 and r 5 are taken separately and r 1 , r 2 , r 3 and r 4 are each independently hydrogen , ( c 1 - c 6 ) alkyl , halo , cf 3 , oh or or 7 and r 5 is methyl or ethyl ; or ( b ) r 2 and r 5 are , taken together , thereby forming a chroman - 4 - ol ring , and r 1 , r 3 and r 4 are each independently hydrogen , ( c 1 - c 6 ) alkyl , halo , cf 3 , oh or or 7 ; r 6 is r 7 is methyl , ethyl , isopropyl or n - propyl ; r 8 is phenyl optionally substituted with up to three substituents independently selected from the group consisting of ( c 1 - c 6 ) alkyl , halo and cf 3 ; x is o , s or ( ch 2 ) n ; and n is 0 , 1 , 2 , or 3 . and enantiomers of any of the aforementioned compounds ; and pharmaceutically acceptable acid addition salts of any of the aforementioned compounds and of any of their enantiomers . the compounds of formula i can be prepared as follows . the compounds of formula i wherein r 2 and r 5 are taken together forming a chroman - 4 - ol ring , and r 1 , r 3 , and r 4 are hydrogen , can be prepared by one or more of the synthetic methods described and referred to in u . s . pat . no . 5 , 356 , 905 ( incorporated herein by reference , supra ). the compounds of formula i wherein r 2 and r 5 are taken separately , and r 1 , r 2 , r 3 and r 4 are hydrogen can be prepared by one or more of the synthetic methods described and referred to in u . s . pat . nos . 5 , 185 , 343 ; 5 , 272 , 160 ; and 5 , 338 , 754 ; all of which are incorporated herein by reference in their entireties . the compounds of formula i can also be prepared by one or more of the synthetic methods described and referred to in u . s . patent application ser . no . 08 / 292 , 651 ; u . s . pat . no . 5 , 744 , 483 ( issued apr . 28 , 1998 ) and u . s . pat . no . 6 , 008 , 233 ( issued dec . 28 , 1999 ); pct international application no . pct / ib95 / 00398 which designates the united states ( filed may 26 , 1995 ) ( corresponding to wo 96 / 37222 ); and pct international application no . pct / ib95 / 00380 which designates the united states ( filed may 18 , 1995 ) ( corresponding to wo 96 / 06081 ). these united states patents and pct international applications , and the united states patent application , are also all incorporated by reference herein in their entireties . a preferred compound , ( 1s , 2s )- 1 -( 4 - hydroxyphenyl )- 2 -( 4 - hydroxy - 4 - phenylpiperidin - 1 - yl )- 1 - propanol (( 1s , 2s ) free base ), and its tartrate salt , can be prepared as described in u . s . pat . no . 5 , 272 , 160 , referred to above . the resolution of racemic 1 -( 4 - hydroxyphenyl )- 2 -( 4 - hydroxy - 4 - phenylpiperidin - 1 - yl )- 1 - propanol to form the ( 1s , 2s ) free base and the corresponding ( 1r , 2r ) enantiomer can be carried out as described in u . s . pat . no . 6 , 008 , 233 ( issued dec . 28 , 1999 ), referred to above , and as exemplified in example 1 below . the anhydrous mesylate of the ( 1s , 2s ) free base can be prepared as described in u . s . pat . no . 5 , 272 , 160 , referred to above . the anhydrous mesylate of the ( 1s , 2s ) free base , when equilibrated in an 81 % relative humidity environment , will convert to the mesylate salt trihydrate of the ( 1s , 2s ) enantiomer . the mesylate salt trihydrate of ( 1s , 2s )- 1 -( 4 - hydroxyphenyl )- 2 -( 4 - hydroxy - 4 - phenylpiperidin - 1 - yl )- 1 - propanol can be prepared from the ( 1s , 2s ) free base as described in the u . s . pat . no . 6 , 008 , 233 , entitled “( 1s , 2s )- 1 -( 4 - hydroxyphenyl )- 2 -( 4 - hydroxy - 4 - phenylpiperidin - 1 - yl )- 1 - propanol methanesulfonate trihydrate ”, referred to above and incorporated herein by reference in its entirety . in this method , ( 1s , 2s ) free base is dissolved in water at 30 ° c . to this solution is added at least 1 equivalent of methane sulfonic acid and the resulting mixture is warmed to 60 - 65 ° c . the warm solution can be filtered to render it particulate free . the solution is concentrated to approximately 40 % of the initial volume , cooled below 10 ° c ., isolated by filtration and dried to a water content ( measured karl fischer titration ) of approximately 11 . 3 %. the resulting crystalline mesylate salt trihydrate can be further purified by recrystallization . another preferred compound , ( 3r , 4s )- 3 -[ 4 -( 4 - fluorophenyl )- 4 - hydroxy - piperidin - 1 - yl ]- chroman - 4 , 7 - diol (( 3r , 4s ) chromanol ), can be prepared as described in u . s . pat . nos . 5 , 356 , 905 , 5 , 744 , 483 ( issued apr . 28 , 1998 ), and u . s . provisional patent application entitled “ process for the resolution of cis - racemic 7 - benzyloxy - 3 -[ 4 -( 4 - fluorophenyl )- 4 - hydroxy - piperidin - 1 - yl ]- chroman - 4 - ol dibenzoyl - d - tartrate ”, all three of which are referred to above . the starting materials and reagents required for the synthesis of the ( 3r , 4s ) chromanol are readily available , either commercially , according to synthetic methods disclosed in the literature , or by synthetic methods exemplified in the description provided below . the ( 3r , 4s ) chromanol can be prepared by fractional crystallization of the l - proline ester of racemic cis - 7 - benzyloxy - 3 -[ 4 -( 4 - fluorophenyl )- 4 - hydroxy - piperidin - 1 - yl ]- chroman - 4 - ol , as described in u . s . pat . no . 5 , 744 , 483 , referred to above . in a preferred method , the resolution method described in u . s . provisional patent application entitled “ process for the resolution of cis - racemic 7 - benzyloxy - 3 -[ 4 -( 4 - fluorophenyl )- 4 - hydroxy - piperidin - 1 - yl ]- chroman - 4 - ol dibenzoyl - d - tartrate ”, referred to above , and as exemplified in example 3 . in this method , the parent chromanol is prepared by dissolving racemic cis - 7 - benzyloxy - 3 -[ 4 -( 4 - fluorophenyl )- 4 - hydroxy - piperidin - 1 - yl ]- chroman - 4 - ol with an equal molar amount of dibenzoyl - d - tartaric acid in boiling aqueous ethanol . racemic cis - 7 - benzyloxy - 3 -[ 4 -( 4 - fluorophenyl )- 4 - hydroxy - piperidin - 1 - yl ]- chroman - 4 - ol is prepared as described in u . s . patent application ser . no . 08 / 189 , 479 , referred to above . the concentration of aqueous ethanol is not critical and may be varied between 75 % and 95 % ethanol ( etoh ). a concentration of 9 : 1 / etoh : h 2 o has been found to be effective and is preferred . a sufficient amount of the aqueous ethanol solvent to dissolve the racemic compound is required . this amount has been found to be about 17 ml per gram of racemic compound . upon stirring while heating under reflux , the racemic compound dissolves to form a hazy solution which is allowed to cool with stirring whereupon the (+) isomer , ( 3r , 4s )- 7 - benzyloxy - 3 -[ 4 -( 4 - fluorophenyl )- 4 - hydroxy - piperidin - yl ]- chroman - 4 - ol dibenzoyl - d - tartrate , precipitates and may be collected by filtration and washed with aqueous ethanol . this is the tartrate salt of the ( 3r , 4s ) chromanol . the lactate and mandelate salts of the ( 3r , 4s ) chromanol are prepared in an analogous manner . this initial product is of about 90 % optical purity . if a higher purity is desired , the product may be heated again with aqueous ethanol , cooled and the product collected and washed . two such treatments were found to yield the (+) isomer of 99 . 4 % optical purity in an overall yield of 74 %. this method avoids a reduction step with lithium aluminum hydride and is therefore preferable for bulk operations . this method also can produce a significantly higher yield of the desired product . the above described (+) isomer can be converted to ( 3r , 4s )- 3 -[ 4 -( 4 - fluorophenyl )- 4 - hydroxy - piperidin - 1 - yl ]- chroman - 4 , 7 - diol by standard procedures . for example , treatment with dilute base can be used to free the piperidinyl base and subsequent hydrogeneration removes the 7 - benzyl group to yield the ( 3r , 4s ) chromanol . nr2b subunit selective nmda receptor antagonists useful in the practice of the invention may also be used in the form of a pharmaceutically acceptable salt . the expression “ pharmaceutically - acceptable acid addition salts ” is intended to include but not be limited to such salts as the hydrochloride , hydrobromide , sulfate , hydrogen sulfate , phosphate , hydrogen phosphate , dihydrogenphosphate , acetate , succinate , citrate , tartrate , lactate , mandelate , methanesulfonate ( mesylate ) and p - toluenesulfonate ( tosylate ) salts . the acid addition salts of the compounds of the present invention are readily prepared by reacting the base forms with the appropriate acid . when the salt is of a monobasic acid ( e . g ., the hydrochloride , the hydrobromide , the p - toluenesulfonate , the acetate ), the hydrogen form of a dibasic acid ( e . g ., the hydrogen sulfate , the succinate ) or the dihydrogen form of a tribasic acid ( e . g ., the dihydrogen phosphate , the citrate ), at least one molar equivalent and usually a molar excess of the acid is employed . however when such salts as the sulfate , the hemisuccinate , the hydrogen phosphate or the phosphate are desired , the appropriate and exact chemical equivalents of acid will generally be used . the free base and the acid are usually combined in a co - solvent from which the desired salt precipitates , or can be otherwise isolated by concentration and / or addition of a non - solvent . any other compound that is an nr2b subunit selective nmda receptor antagonist , including its pharmaceutically acceptable salts , can be used in the methods of this invention . nmda receptor antagonists having nr2b subunit selectivity that may be used according to the present invention are , for example , described in u . s . pat . nos . 6 , 046 , 213 ; 5 , 185 , 343 ; 5 , 272 , 160 , 5 , 338 , 754 ; and 5 , 356 , 905 ( which issued , respectively , on apr . 4 , 2000 ; feb . 9 , 1993 ; dec . 21 , 1993 ; aug . 16 , 1994 ; and oct . 18 , 1994 ); u . s . pat . no . 6 , 046 , 213 ( issued apr . 4 , 2000 ), u . s . pat . no . 5 , 744 , 483 ( issued apr . 28 , 1998 ) and u . s . pat . no . 6 , 008 , 233 ( issued dec . 28 , 1999 ); pct international application no . pct / ib95 / 00398 ( filed may 26 , 1995 , corresponding to wo 96 / 37222 ); and pct international application no . pct / ib95 / 00380 ( filed may 18 , 1995 , corresponding to wo 96 / 06081 ). other nr2b subunit selective nmda receptor antagonists that may be used according to the present invention are described in wo 97 / 32581 ( international publication date sep . 12 , 1997 ), wo 98 / 18793 ( international publication date may 7 , 1998 ), wo 97 / 23202 ( international publication date jul . 3 , 1997 ), ep 0 824 098 a1 ( date of publication , feb . 18 , 1998 ), ep 0846 683 a1 ( date of publication , jun . 10 , 1998 ), and de 19739331 ( published nov . 26 , 1998 ). all of the foregoing patents and published patent applications are incorporated by reference herein in their entireties . other compounds that are indicated to bind selectively to nr2b nmda receptor subunits that may be used according to the present invention are ifenprodil , supra , eliprodil ( described in u . s . pat . no . 4 , 690 , 931 ( issued sep . 1 , 1987 ); and compounds described in wo 97 / 23458 ( international publication date jul . 3 , 1997 ), wo 97 / 23216 ( international publication date jul . 3 , 1997 ); wo 97 / 23215 ( international publication date jul . 3 , 1997 ); and wo 97 / 23214 ( international publication date jul . 3 , 1997 ). the preceding u . s . patent and pct international applications are incorporated by reference herein in their entireties . wo 97123458 discloses 2 - substituted piperidine analogs . examples of these analogs include n -( methoxycarbonylbutyl )- 4 - benzylpiperidine , 4 - benzylpiperidylpentamide , 4 - benzylpiperidylpentahydrazide , n -( 5 -( 4 - benzylpiperidin - 1 - yl ) valeroyl )- n ′-( 4 - nitrobenzoyl ) hydrazine , n -( 4 - aminobenzoyl )- n ′-( 5 -( 4benzylpiperidin - 1 - yl ) valeroyl ) hydrazine , 4 - benzyl - 1 -( 3 - butynyl ) piperidine , 1 -( 3 - butynyl )- 4 -( p - chlorophenyl )- 4 - hydroxypiperidine , m - fluorobenzyltriphenylphosphonium bromide , 1 - benzyl - 4 -( m - fluorobenzylidene ) piperidine , 4 -( 4 - benzylpiperidinyl )- 4 ′- fluorobenzophenone and 4 , 4 ′- bis ( 4 - benzylplperidinyl ) benzophenone . wo 97 / 23216 discloses 4 - substituded piperidine analogs . examples of these analogs include 4 - benzyl - 1 -( 2 - phenoxyethyl ) piperidine , 4 - benzyl - 1 -( 3 - phenoxypropyl ) piperidine , 4 - benzyl - 1 -[ 2 - hydroxy - 3 -( 1 - naphthyloxy ) propyl ] piperidine , 4 - benzyl - 1 -[( 2 - hydroxy - 4 - phenyl ) butyl ] piperidine , 4 - phenoxy - 1 -[( 4 - fluorophenoxy ) propyl ] piperidine , 4 -( 2 - methoxyphenoxy )- 1 -( 4 - phenylbutyl ) piperidine , 1 -( 3 - phenoxypropyl )- 4 - phenylpiperidine , 1 -( 2 - phenoxyethyl )- 4 - phenylpiperidine , 1 -( 4 - phenoxybutyl )- 4 - phenylpiperidine , and 1 -( 4 -( 3 -( trifluoromethyl ) phenoxy ) butyl )- 4 - phenylpiperidine hydrobromide . wo 97 / 23215 discloses 2 - substituted piperidine analogs . examples of these analogs include2 - benxylpiperidine hydrochloride , 1 , 2 - dibenzylpiperidine , hydrobromide , 2 - benzyl - 1 -( 2 - phenylethyl ) piperidine , hydrobromide , 2 - benzyl - 1 -( 3 - phenylpropyl ) piperidine , hydrobromide , 2 - benzyl - 1 -( 4 - phenylbutyl ) piperidine ), citric acid salt , 2 - benzyl - 1 -( 2 - phenoxyethyl ) piperidine , citric acid salt , 2 - benzyl - 1 -( 3 - phenoxypropyl ) piperidine hydrobromide , 2 - benzyl - 1 -( 4 - phenoxybutyl ) piperidine hydrobromide , and 4 -( o -( trifluoromethyl ) phenoxy )- 1 - bromobutane . wo 97 / 23214 discloses 4 - substituded piperidine analogs , including hydroxypiperidine and tetrahydropyridine analogs . examples of these analogs include 1 -( 3 - butynyl )- 4 -( 4 - chlorobenzyl ) piperidine , 1 -( 3 - butynyl )- 4 -[( 4 - trifluoromethylphenyl ) methyl ] piperidine , 4 -( 4 - chloro ) benzyl - 1 -[ 4 -( 3 - aminophenyl )- 3 - butynyl ]- piperidine , 4 -( 4 - trifluoromethyl ) benzyl - 1 -[ 4 -( 3 - aminophenyl )- 3 - butynyl ]- piperidine , 1 -( t - butyldimethylsiloxy )- 4 -( 3 - amino - phenyl )- 3 - butynyl , 1 - tosyl - 4 -( 3 - aminophenyl )- 3 - butyne , 1 -[ 4 -( 5 -( 2 - amino ) pyridynyl )- 3 - butynyl ]- 4 - hydroxy - 4 -( 4 - chlorophenyl ) piperidine , 1 -[ 4 -( 3 - aminophenyl )- 3 - butynyl ]- 4 - hydroxy - 4 -( 4 - piperidine , 1 -( t - butyldimethylsiloxy )- 4 -( 3 - amino - phenyl )- 3 - butyne , 1 - tosyl - 4 -( 3 - aminophenyl )- 3 - butyne , 1 -[ 4 -( 5 -( 2 - amino ) pyridynyl )- 3 - butynyl ]- 4 - hydroxy - 4 -( 4 - chlorophenyl ) piperidine , 1 -[ 4 -( 3 - aminophenyl )- 3 - butynyl ]- 4 - hydroxy - 4 -( 4 - chlorophenyl ) piperidine , 1 -[ 4 -( 3 - aminophenyl )- 3 - butynyl ]- 4 -( 4 - chlorophenyl )- 1 , 2 , 5 , 6 - tetrahydropyridine , and 1 -[ 4 -( 5 -( 2 - amino ) pyridynyl )- 3 - butynyl ]- 4 -( 4 - chlorophenyl )- 1 , 2 , 5 , 6 - tetrahydropyridine . compounds that selectively antagonize nmda receptors comprising an nr2b subunit by specifically binding to the nr2b subunit can be determined by screening compounds for inhibition of nmda - induced current in recombinant xenopus oocytes cotransfected with the nr1a subunit and the nr2b subunit ( see , e . g ., monyer , et al ., science , 1992 , 256 : 1217 - 1221 ). a compound &# 39 ; s activity in inhibiting current in the recombinant cells comprising the nr2b subunit can be compared to its activity inhibiting nmda - induced current in recombinant xenopus oocytes expressing the nr1 subunit and nr2a , nr2c , and nr2d subunits . ( see , chenard and menniti , supra ). one general method that can also generally predict whether or not a compound has nr2b subunit selectivity , for purposes of the present invention , is a standard competitive binding assay using [ 3 h ] radiolabeled racemic cp - 101 , 606 ( which contains [ 3 h ](+)-( 1s , 2s )- 1 -( 4 - hydroxy - phenyl )- 2 -( 4 - hydroxy - 4 - phenylpiperidino )- 1 - propanol ; see , for example , u . s . pat . no . 6 , 046 , 213 ). if a compound has an ic 50 of less than about 5 μm for inhibition of racemic [ 3 h ] cp - 101 , 606 binding to the nr2b subunit , than the compound has nr2b subunit selectivity for purposes of the present invention . an example of such an assay is as follows : example of nr2b subunit binding assay . selectivity of compounds for the nr2b - subunit containing nmda receptor can be defined as an affinity for the racemic [ 3 h ] cp - 101 , 606 binding site in forebrain of rats , as described in chenard and menniti , supra . this affinity is assessed in a radioligand binding assay as described below . selective compounds are preferably those which displace specific binding of racemic [ 3 h ] cp - 101 , 606 from rat forebrain membranes with an ic 50 of about ≦ 5 μm . the binding of racemic [ 3 h ](+)-( 1s , 2s )- 1 -( 4 - hydroxy - phenyl )- 2 -( 4 - hydroxy - 4 - phenylpiperidino )- 1 - propanol to rat forebrain membranes is measured as described by menniti et al . ( cp - 101 , 606 , a potent neuroprotectant selective for forebrain neurons , european journal of pharmacology , 1997 , 331 : 117 - 126 ). forebrains of adult male cd rats are homogenized in 0 . 32m sucrose at 4 ° c . the crude nuclear pellet is removed by centrifugation at 1 , 000 × g for 10 min ., and the supernatant centrifuged at 17 , 000 × g for 25 min . the resulting pellet is resuspended in 5 mm tris acetate ph 7 . 4 at 4 ° c . for 10 min . to lyse cellular particles and again centrifuged at 17 , 000 × g . the resulting pellet is washed twice in tris acetate , resuspended at 10 mg protein / ml and stored at − 20 ° c . until use . for binding assays , membranes are thawed , homogenized , and diluted to 0 . 5 mg protein / ml with 50 mm tris hcl , ph 7 . 4 . compounds under study are added at various concentrations followed by racemic [ 3 h ] cp - 101 , 606 ( specific activity 42 . 8 ci / mmol , 5 nm final concentration ). following incubation for 20 min at 30 ° c . in a shaking water bath , samples are filtered onto whatman gfb glass fiber filters using a mb - 48r cell harvester ( brandel research and development laboratories , gaithersburg md .). filters are washed for 10 s with ice cold tris hcl buffer and the radioactivity trapped on the filter quantified by liquid scintillation spectroscopy . nonspecific binding is determined in parallel incubations containing 100 μm racemic cp - 101 , 606 . specific binding is defined as total binding minus nonspecific binding . in one embodiment of the present invention , an nr2b subunit selective nmda antagonist is furthermore selective for nr2b subunit - containing nmda receptors over α 1 - adrengergic receptors . for example , although ifenprodil ( supra ) has selectivity for the nr2b subtype of nmda receptor , this compound is also a well known α 1 - adrenergic receptor antagonist . ( carter et al . j . pharmacol . exp . ther ., 235 , 475 - 482 ( 1990 )). compounds that antagonize α 1 - adrengergic receptors can cause a reduction in blood pressure that can be a complication to therapeutic use . preferably , the nmda antagonist has a ratio of nr2b receptor activity to α 1 - adrenergic receptor activity of at least about 3 : 1 , more preferably at least about 5 : 1 . affinity for the nr2b subunit containing nmda receptor is measured as the ic 50 for displacement of specific binding of racemic [ 3 h ](+)-( 1s , 2s )- 1 -( 4 - hydroxy - phenyl )- 2 -( 4 - hydroxy - 4 - phenylpiperidino )- 1 - propanol from rat forebrain membranes ( described above ). affinity for the α 1 - adrengergic receptor is defined as the ic 50 for displacement of specific binding of racemic [ 3 h ] prazosin from rat brain membranes , measured as described by greengrass and bremner ( binding characteristics of [ 3 h ] prazosin to rat brain α - adrenergic receptors , european journal of pharmacology , 55 , 323 - 326 , ( 1979 )). a compound with a ratio of ([ 3 h ] prazosin /[ 3 h ](+)-( 1s , 2s )- 1 -( 4 - hydroxy - phenyl )- 2 -( 4 - hydroxy - 4 - phenylpiperidino )- 1 - propanol ) affinity greater than three is considered selective . forebrains of adult male sprague dawley rats are homogenized in 20 volumes of ice cold 50 mm tris / hcl buffer ( ph 7 . 7 ). the homogenate is centrifuged at 50 , 000 × g for 10 min . at 4 ° c . the pellet is resuspended and centrifuged under identical conditions and the final pellet is resuspended in 80 volumes of 50 mm tris / hcl ( ph 8 . 0 ) at 4 ° c . for binding assays , compounds under study are added at various concentrations to 500 μg membrane protein in 1 ml of 50 mm tris / hcl buffer , followed by [ 3 h ] prazosin ( amersham , specific activity 33 ci / mmol , 0 . 2 nm final concentration ). following incubation for 30 min at 25 ° c . in a shaking water bath , samples are filtered onto whatman gfb glass fiber filters using a mb - 48r cell harvester ( brandel research and development laboratories , gaithersburg md .). filters are washed three times for 10 s with ice cold tris hcl buffer and the radioactivity trapped on the filter quantified by liquid scintillation spectroscopy . nonspecific binding is determined in parallel incubations containing 100nm prazosin . specific binding is defined as total binding minus nonspecific binding . an effective amount of the nr2b subunit selective nmda antagonist for use on the present invention is typically from about 0 . 02 to 250 mg / kg / day ( 0 . 001 - 12 . 5 g / day in a typical human weighing 50 kg ) in single or divided doses , regardless of route of administration . a more preferred dosage range is from about 0 . 15 mg / kg / day to about 250 mg / kg / day . of course , depending on the specific circumstances ( for example , the presence or absence of a predisposition to the disease or condition being treated , the severity or expected severity of the disease , or the age or general health of the patient ), even doses outside the aforementioned ranges may be in order . the particular dose given the specific circumstances can be determined by a physician or other health - care professional of ordinary skill . the nr2b subunit selective nmda receptor antagonist useful in the method of the present invention is generally administered in the form of a pharmaceutical composition comprising one or more nr2b subunit selective nmda receptor antagonists together with a pharmaceutically acceptable carrier or diluent . the compositions described herein useful in the present invention are generally formulated in a conventional manner utilizing solid or liquid vehicles or diluents as appropriate to the mode of administration . for purposes of oral administration , tablets containing excipients such as sodium citrate , calcium carbonate and dicalcium phosphate may be employed along with various disintegrants such as starch and preferably potato or tapioca starch , alginic acid and certain complex silicates , together with binding agents such as polyvinylpyrrolidone , sucrose , gelatin and acacia . additionally , lubricating agents such as , but not limited to , magnesium stearate , sodium lauryl sulfate and talc are often very useful for tableting purposes . solid compositions of a similar type may also be employed as fillers in soft elastic and hard - filled gelatin capsules ; preferred materials in this connection also include , by way of example and not of limitation , lactose or milk sugar as well as high molecular weight polyethylene glycols . when aqueous suspensions and / or elixirs are desired for oral administration , the essential active ingredient may be combined with various sweetening or flavoring agents , coloring matter or dyes and , if so desired , emulsifying and / or suspending agents , together with diluents such as water , ethanol , propylene glycol , glycerin and various like combinations thereof . the present invention is illustrated by the following examples , but is not limited to the details thereof . all nonaqueous reactions were run under nitrogen for convenience and generally to maximize yields . all solvents / diluents were dried according to standard published procedures or purchased in a predried form . all reactions were stirred either magnetically or mechanically . nmr spectra are recorded at 300 mhz and are reported in ppm . the nmr solvent was cdcl 3 unless otherwise specified . ir spectra are reported in cm 1 , generally specifying only strong signals . (+)- tartaric acid ( 300 mg , 2 mmol ) was dissolved in 30 ml warm methanol . racemic 1 s *, 2 s *- 1 -( 4 - hydroxyphenyl )- 2 -( 4 - hydroxy - 4 - phenylpiperidin - 1 - yl )- 1 - propanol ( 655 mg , 2 mmol ) was added all at once . with stirring and gentle warming a colorless homogeneous solution was obtained . upon standing at ambient temperature 24 hours , 319 mg ( 66 %) of a fluffy white precipitate was obtained . this product was recrystallized from methanol to give 263 mg of the (+)- tartrate salt of levorotatory title product as a white solid ; mp 206 . 5 - 207 . 5 ° c . ; [ alpha ] d = 36 . 2 °. this salt ( 115 mg ) was added to 50 ml of saturated nahco 3 . ethyl acetate ( 5 ml ) was added and the mixture was vigorously stirred 30 minutes . the aqueous phase was repeatedly extracted with ethyl acetate . the organic layers were combined and washed with brine , dried over calcium sulfate , and concentrated . the tan residue was recrystallized from ethyl acetate - hexane to give 32 mg ( 39 %) of white , levorotatory title product ; mp 203 - 204 ° c . ; [ alpha ] d =− 58 . 4 °. anal . calc &# 39 ; d . for c 20 h 25 no 3 ; c , 73 . 37 ; h , 7 . 70 ; n , 4 . 28 . found : c , 72 . 61 ; h , 7 . 45 ; n , 4 . 21 . the filtrate from the (+)- tartrate salt preparation above was treated with 100 ml saturated aqueous nahco 3 and extracted well with ethyl acetate . the combined organic extracts were washed with brine , dried over calcium sulfate and concentrated to give 380 mg of recovered starting material ( partially resolved ). this material was treated with (−)- tartaric acid ( 174 mg ) in 30 ml of methanol as above . after standing for 24 hours , filtration gave 320 mg ( 66 %) of product which was further recrystallized from methanol to produce 239 mg of the (−)- tartrate salt of dextrorotatory title product ; mp 206 . 5 - 207 . 5 ° c . [ alpha ] d =+ 33 . 9 °. the latter was converted to dextrorotatory title product in the manner above in 49 % yield ; mp 204 - 205 ° c . ; [ alpha ] d =+ 56 . 9 °. anal . found : c , 72 . 94 ; h , 7 . 64 ; n , 4 . 24 . a 50 gallon glass lined reactor was charged with 17 . 1 gallons of acetone , 8 . 65 kilograms ( kg ) ( 57 . 7 mol ) of 4 ′- hydroxypropiophenone , 9 . 95 kg ( 72 . 0 mol ) of potassium carbonate and 6 . 8 liters ( l ) ( 57 . 7 mol ) of benzylbromide . the mixture was heated to reflux ( 56 ° c .) for 20 hours . analysis of thin layer chromatography ( tlc ) revealed that the reaction was essentially complete . the suspension was atmospherically concentrated to a volume of 10 gallons and 17 . 1 gallons of water were charged . the suspension was granulated at 25 ° c . for 1 hour . the product was filtered on a 30 ″ lapp and washed with 4 . 6 gallons of water followed by a mixture of 6 . 9 gallons of hexane and 2 . 3 gallons of isopropanol . after vacuum drying at 45 ° c ., this yielded 13 . 35 kg ( 96 . 4 %) of the above - depicted product . a second run was carried out with 9 . 8 kg ( 65 . 25 mol ) of 4 ′- hydroxypropiophenone using the procedure described above . after drying 15 . 1 kg ( 96 . 3 %) of the above - depicted product was obtained . under a nitrogen atmosphere , a 100 gallon glass lined reactor was charged with 75 gallons of methylene chloride and 28 . 2 kg ( 117 . 5 mol ) of the product from step 1 . the solution was stirred five minutes and then 18 . 8 kg of bromine was charged . the reaction was stirred for 0 . 5 hours at 22 ° c . analysis of tlc revealed that the reaction was essentially complete . to the solution was charged 37 gallons of water and the mixture was stirred for 15 minutes . the methylene chloride was separated and washed with 18 . 5 gallons of saturated aqueous sodium bicarbonate . the methylene chloride was separated , atmospherically concentrated to a volume of 40 gallons and 60 gallons of isopropanol was charged . the concentration was continued until a pot temperature of 80 ° c . and final volume of 40 gallons were obtained . the suspension was cooled to 20 ° c . and granulated for 18 hours . the product was filtered on a 30 ″ lapp and washed with 10 gallons of isopropanol . after vacuum drying at 45 ° c ., this yielded 29 . 1 kg ( 77 . 6 %) of the above - depicted product . under a nitrogen atmosphere , a 20 gallon glass lined reactor was charged with 4 . 90 kg ( 15 . 3 mol ) of the product from step 2 , 7 . 0 gallons of ethyl acetate , 2 . 70 kg ( 15 . 3 mol ) of 4 - hydroxy - 4 - phenylpiperidine and 1 . 54 kg of triethylamine ( 15 . 3 mol ). the solution was heated to reflux ( 77 ° c .) for 18 hours . the resulting suspension was cooled to 20 ° c . analysis by tlc revealed that the reaction was essentially complete . the byproduct ( triethylamine hydrobromide salt ) was filtered on a 30 ″ lapp and washed with 4 gallons of ethyl acetate . the filtrate was concentrated under vacuum to a volume of 17 liters . the concentrate was charged to 48 liters of hexane and the resulting suspension granulated for 2 hours at 20 ° c . the product was filtered on a 30 ″ lapp and washed with 4 gallons of hexane . after vacuum drying at 50 ° c ., this yielded 4 . 9 kg ( 77 %) of the above - depicted product . a second run was carried out with 3 . 6 kg ( 11 . 3 mol ) of the product from step 2 using the procedure described above . after drying 4 . 1 kg ( 87 %) of the above - depicted product was obtained . under a nitrogen atmosphere , a 100 gallon glass lined reactor was charged with 87 . 0 gallons of 2b ethanol and 1 . 7 kg ( 45 . 2 mol ) of sodium borohydride . the resulting solution was stirred at 25 ° c . and 9 . 4 kg ( 22 . 6 mol ) of the product from step 3 was charged . the suspension was stirred for 18 hours at 25 - 30 ° c . analysis by tlc revealed that the reaction was essentially complete to the desired threo diastereoisomer . to the suspension was charged 7 . 8 liters of water . the suspension was concentrated under vacuum to a volume of 40 gallons . after granulating for 1 hour , the product was filtered on a 30 ″ lapp and washed with 2 gallons of 2b ethanol . the wet product , 9 . 4 gallons of 2b - ethanol and 8 . 7 gallons of water were charged to a 100 gallon glass lined reactor . the suspension was stirred at reflux ( 78 ° c .) for 16 hours . the suspension was cooled to 250 ° c ., filtered on 30 ″ lapp and washed with 7 gallons of water followed by 4 gallons of 2b ethanol . after air drying at 50 ° c ., this yielded 8 . 2 kg ( 86 . 5 %) of the above - depicted product . this material was recrystallized in the following manner . a 100 gallon glass lined reactor was charged with 7 . 9 kg ( 18 . 9 mol ) of the product from step 3 , 20 gallons of 2b ethanol and 4 gallons of acetone . the suspension was heated to 70 ° c . producing a solution . the solution was concentrated atmospherically to a volume of 15 gallons . the suspension was cooled to 25 ° c . and granulated for 1 hour . the product was filtered on a 30 ″ lapp . the wet product and 11 . 7 gallons of 2b ethanol was charged to a 100 gallon glass lined reactor . the suspension was heated to reflux ( 78 ° c .) for 18 hours . the suspension was cooled to 25 ° c ., filtered on a 30 ″ lapp and washed with 2 gallons of 2b ethanol . after air drying at 50 ° c . this yielded 5 . 6 kg ( 70 . 6 %) of the above - depicted product . under a nitrogen atmosphere , a 50 gallon glass lined reactor was charged with 825 g of 10 % palladium on carbon ( 50 % water wet ), 5 . 5 kg ( 13 . 2 mol ) of the product from step 4 and 15 . 5 gallons of tetrahydrofuran ( thf ). the mixture was hydrogenated between 40 - 50 ° c . for 2 hours . at this time , analysis by tlc revealed that the reduction was essentially complete . the reaction was filtered through a 14 ″ sparkler precoated with celite and washed with 8 gallons of thf . the filtrate was transferred to a clean 100 gallon glass lined reactor , vacuum concentrated to a volume of 7 gallons and 21 gallons of ethyl acetate were charged . the suspension was atmospherically concentrated to a volume of 10 gallons and a pot temperature of 72 ° c . the suspension was cooled to 10 ° c ., filtered on a 30 ″ lapp and washed with 2 gallons of ethyl acetate . after air drying at 55 ° c . this yielded a 3 . 9 kg ( 90 %) of the above - depicted product ( i . e ., the free base ). a 100 gallon glass lined reactor was charged with 20 gallons of methanol and 3 . 7 kg ( 11 . 4 mol ) of the product from step 5 ( i . e ., the free base ). the suspension was heated to 60 ° c . and 1 . 7 kg ( 11 . 4 mol ) of d -(−)- tartaric acid were charged . the resulting solution was heated to reflux ( 65 ° c .) for 3 hours after which a suspension formed . the suspension was cooled to 35 ° c ., filtered on a 30 ″ lapp and washed with 1 gallon of methanol . the wet solids were charged to a 100 gallon glass lined reactor with 10 gallons of methanol . the suspension was stirred for 18 hours at 25 ° c . the suspension was filtered on a 30 ″ lapp and washed with 2 gallons of methanol . after air drying at 50 ° c . this yielded 2 . 7 kg ( 101 %) of the above - depicted product ( i . e ., the tartaric acid salt of the free base ( r -(+)- enantiomer )). this material was purified in the following manner : a 100 gallon glass lined reactor was charged with 10 . 6 gallons of methanol and 2 . 67 kg ( 5 . 6 mol ) of the above tartaric acid salt . the suspension was heated to reflux ( 80 ° c .) for 18 hours . the suspension was cooled to 30 ° c ., filtered on a 30 ″ lapp and washed with 4 gallons of methanol . after air drying at 50 ° c ., this yielded 2 . 05 kg ( 76 . 7 %) of the above - depicted product ( i . e ., the tartaric acid salt of the free base ). a 55 liter nalgene tub was charged with 30 liters of water and 1056 g ( 12 . 6 mol ) of sodium bicarbonate at 20 ° c . to the resulting solution was charged 2 . 0 kg ( 4 . 2 mol ) of the product from step 6 ( i . e ., the tartaric acid salt of the free base ). the suspension was stirred for 4 hours during which a great deal foaming occurred . after the foaming ceased , the suspension was filtered on a 32 cm funnel and washed with 1 gallon of water . after air drying at 50 ° c ., this yielded 1 . 28 kg ( 93 . 5 %) of the above - depicted product ( i . e ., the free base ). a 22 liter flask was charged with 1277 g ( 3 . 9 mol ) of product from step 7 and 14 liters of water . the suspension was warmed to 30 ° c . and 375 g ( 3 . 9 mol ) of methane sulfonic acid were charged . the resulting solution was warmed to 60 ° c ., clarified by filtering through diatomaceous earth ( celite ™) and washed with 2 liters of water . the speck - free filtrate was concentrated under vacuum to a volume of 6 liters . the suspension was cooled to 0 - 5 ° c . and granulated for 1 hour . the product was filtered on an 18 ″ filter funnel and washed with 635 ml of speck - free water . after air drying at 25 ° c . for 18 hours , this yielded 1646 g ( 88 %) of the above - depicted product ( i . e ., the mesylate salt trihydrate ). a mixture of 3 - methyl - 4 - triisopropylsilyloxy - ε - bromopropiophenone ( 9 . 17 g , 22 . 97 mmol ), 4 -( 4 - fluorophenyl )- 4 - hydroxypiperidine ( 6 . 73 g , 34 . 45 mmol ) and triethylamine ( 8 . 0 ml , 57 . 43 mmol ) in in ethanol ( 180 ml ) was refluxed for 6 hours . the solvent was removed at reduced pressure and the residue was partitioned between ethyl acetate and water . the phases were separated and the organic layer was washed with brine , dried over calcium sulfate and concentrated . the residue was flash chromatographed on silica gel ( 3 × 3 . 5 inches packed in hexane ) with elution proceeding as follows : 10 % ethyl acetate / hexane ( 1000 ml ), nil ; 20 % ethyl acetate / hexane ( 700 ml ), nil ; 20 % ethyl acetate / hexane ( 1300 ml ) and 25 % ethyl acetate / hexane ( 600 ml ), 7 . 66 g ( 65 %) of 1 -( 3 - methyl - 4 - triisopropylsilyloxyphenyl )- 2 -( 4 -( 4 - fluorophenyl )- 4 - hydroxypiperidin - 1 - yl )- propan - 1 - one as a yellow foam which was suitable for use without further purification . a sample recrystallization from ethyl acetate / hexane as white crystals had : m . p . 78 - 82 ° c . a mixture of sodium borohydride ( 0 . 564 g , 14 . 92 mmol ) and ethanol ( 60 ml ) was stirred 10 minutes and then 1 -( 3 - methyl - 4 - triisopropylsilyloxyphenyl )- 2 -( 4 -( 4 - fluorophenyl )- 4 - hydroxypiperidin - 1 - yl )- propan - 1 - one ( 7 . 66 g , 14 . 92 mmol in 10 ml of ethanol ) was added with two 30 ml ethanol rinses . the reaction mixture was stirred at ambient temperature overnight . the white solid that precipitated was collected by filtration and dried to yield 5 . 72 g ( 74 %) of ( 1r *, 2r *)- 1 -( 3 - methyl - 4 - triisopropylsilyloxyphenyl )- 2 -( 4 -( 4 - fluorophenyl )- 4 - hydroxypiperidin - 1 - yl )- propan - 1 - ol , which was suitable for use without further purification and had : m . p . 188 - 89 ° c . the product of the above reaction ( 5 . 72 g , 11 . 1 mmol ) was dissolved in tetrahydrofuran ( 150 ml ) and tetrabutylammonium fluoride ( 12 . 21 ml , 12 . 21 mmol , 1m tetrahydrofuran solution ) was added . the reaction was stirred 1 hour at ambient temperature and then concentrated . the residue was partitioned between ethyl acetate and water and the two phases were separated . the organic layer was slurried with methylene chloride . the white solid that precipitated was collected by filtration and dried to afford 3 . 41 g ( 85 %) of ( 1r *, 2r *)- 1 -( 4 - hydroxy - 3 - methylphenyl )- 2 -( 4 -( 4 - fluorophenyl )- 4 - hydroxypiperidin - 1 - yl )- propan - 1 - ol . a sample ( 0 . 16 g , 0 . 447 mmol ) was converted to the corresponding mesylate salt . the salt was slurried in methanol ( 8 ml ) and methanesulfonic acid ( 0 . 029 ml , 0 . 45 mmol ) was added . the mixture was filtered and concentrated . the mixture was then recrystallized from ethanol to give 0 . 152 g ( 58 %) of the mesylate salt which had : m . p . 215 - 216 ° c . analysis calculated for c 21 h 25 fno 3 . ch 4 so 3 : c , 58 . 01 ; h , 6 . 64 , n , 3 . 07 . found : c , 57 . 99 ; h , 6 . 72 ; n , 3 . 17 . a mixture of 2 - bromo - 1 -( 2 , 2 - diphenyl - benzo ( 1 , 3 ) dioxol - 5 - yl )- propan - 1 - one ( 2 . 00 g , 4 . 89 mmol ), 4 - hydroxy - 4 - phenylpiperidine ( 0 . 9 g , 5 . 08 mmol ) and triethylamine ( 1 . 40 ml , 10 . 04 mmol ) in ethanol ( 50 ml ) was refluxed overnight . the solvent was removed at reduced pressure and the residue was partitioned between ether and water . the phases were separated and the organic layer was washed with brine , dried over magnesium sulfate and concentrated . the residue was flash chromatographed on silica gel ( 2 × 5 inches packed with hexane ) with elution proceeding as follows : 20 % ethyl acetate / hexane ( 500 ml ), unweighed forerun ; 50 % ethyl acetate / hexane ( 500 ml ), 1 . 76 g ( 71 %) of 1 -( 2 , 2 )- diphenyl - benzo ( 1 , 3 ) dioxol - 5 - yl )- 2 -( 4 - hydroxy - 4 - phenylpiperidin - 1 - yl )- propan - 1 - one as light tan foam which was suitable for use without further purification and had : nmr δ 7 . 81 ( dd , j = 1 . 7 , 8 . 3 hz , 1h ), 7 . 70 ( d , j = 1 . 6 hz , 1h ), 7 . 64 - 7 . 13 ( m , 15h ), 6 . 92 ( d , j = 8 . 2 hz , 1h ), 4 . 07 ( q , j = 7 . 0 hz , 1h ), 3 . 39 - 3 . 27 ( m , 1h ), 2 . 94 - 2 . 59 ( m , # h ), 2 . 30 - 2 . 04 ( m , 2h ), 1 . 74 ( br t , j = 13 . 2 hz , 2h ), 1 . 30 ( d , j = 6 . 8 hz , 3h ). a mixture of sodium borohydride ( 0 . 15 g , 3 . 97 mmol ) and ethanol ( 5 ml ) was stirred 10 minutes and then 1 -( 2 , 2 - diphenyl - benzo ( 1 , 3 ) dioxol - 5 - yl )- 2 -( 4 - hydroxy - 4 - phenylpiperidin - 1 - yl )- propan - 1 - one ( 1 . 70 g , 3 . 36 mmol in 20 ml of ethanol ) was added . the reaction was stirred at ambient temperature over the weekend . the white precipitate was collected , rinsed with ethanol and ether and air dried to afford 1 . 35 g of crude product . the product was recrystallized from ethanol / ethyl acetate / methylene chloride to give 1 . 05 g ( 61 %) of 1r *, 2r *)- 1 -( 2 , 2 - diphenyl - benzo ( 1 , 3 ) dioxol - 5 - yl )- 2 -( 4 - hydroxy - 4 - phenylpiperidin - 1 - yl )- propan - 1 - ol which had : mp 224 - 224 . 5 ° c . analysis calculated for c 33 h 33 no 4 : c , 78 . 08 ; h , 6 . 55 ; n , 2 . 76 . found : c , 78 . 16 ; h , 6 . 46n , 2 . 72 . a mixture of the product of the above reaction ( 1 . 00 g , 1 . 97 mmol ) and 10 % palladium on carbon ( 0 . 175 g ) in methanol ( 50 ml ) and acetic acid ( 1 . 0 ml ) was hydrogenated at 50 psi ( initial pressure ) for 5 hours at ambient temperature . additional catalyst ( 0 . 18 g ) was added and the hydrogenation was continued overnight . the reaction was filtered through diatomaceous earth and the filter pad was rinsed with methanol . the filtrate was concentrated and the residue was partitioned between ethyl acetate and saturated aqueous bicarbonate and stirred vigorously for 1 hour . the phases were separated and the aqueous layer was extracted with ethyl acetate ( 2 ×). the combined organic layer was washed with water and brine , dried over magnesium sulfate and concentrated . the residue was flash chromatographed on silica gel ( 1 × 4 inches ) with elution proceeding as follows : 20 % ethyl acetate / hexane ( 500 ml ), nil ; 10 % methanol / ethyl acetate ( 250 ml ), 20 % methanol / ethyl acetate ( 250 ml ), and 50 % methanol / ethyl acetate , 0 . 51 g ( 75 %) of a light yellow - green solid . the solid was recrystallized from ethanol to afford ( 1r *, 2r *)- 1 -( 3 , 4 - dihydroxyphenyl )- 2 -( 4 - hydroxy - 4 - phenyl - piperidin - 1 - yl )- propan - 1 - ol as a white solid which had : mp 167 - 168 ° c . analysis calculated for c 20 h 25 no 4 . 0 . 5 c 2 h 6 o : c , 68 . 83 ; h , 7 . 70 ; n , 3 . 82 . found : c , 68 . 78 ; h , 8 . 05 ; n , 3 . 70 . the racemic product was dissolved in ethanol and separated into enantiomers by hplc using the following chromatographic conditions : column , chiralcel od ; mobile phase , 25 % ethanol / 75 % hexane ; temperature , ambient ( approximately 22 ° c . ); detection , uv at 215 nm . under these conditions , 1r , 2r 1 -( 4 - hydroxy - 3 - methoxyphenyl )- 2 -( 4 - hydroxy - 4 - phenyl - piperidin - 1 - yl ) propan - 1 - ol eluted with a retention time of approximately 9 . 12 minuntes and 1s , 2s 1 -( 4 - hydroxy - 3 - methoxyphenyl )- 2 -( 4 - hydroxy - 4 - phenyl - piperidin - 1 - yl ) propan - 1 - ol eluted with a retention time of approximately 16 . 26 minutes . a mixture of 7 - benzyloxy - 3 , 3 - dibromochromanone ( 54 . 7 g , 133 mmol ), 4 -( 4 - fluorophenyl )- 4 - hydroxypiperidine ( 52 . 0 g , 266 mmol ), and triethylamine ( 38 ml , 270 mmol ) in acetonitrile ( 2 . 5 l ) was stirred 16 hours at ambient temperature . a yellow precipitate formed and was collected , washed well with water and ether , and air dried . the yield of 7 - benzyloxy - 3 -{ 4 -( 4 - fluorophenyl )- 4 - hydroxy - piperidine - 1 - yl ]- chromenone was 55 . 4 g ( 93 %) which was suitable for use without further purification . a sample recrystallized from ethanol / tetrahydrofuran had mp 220 - 221 ° c . : nmr dmso ∂ σ δ7 . 99 ( d , j = 9 hz , 2h ), 7 . 56 - 7 . 40 ( m , 8h ), 7 . 18 - 7 . 08 ( m , 4h ), 5 . 25 ( s , 2h ), 5 . 06 ( s , 1h ), 3 . 60 ( br s , 1h ), 3 . 55 - 3 . 35 ( m , 1h , partially obscured by water from the nmr solvent ), 3 . 10 - 2 . 95 ( m , 2h ), 2 . 15 - 2 . 00 ( m , 2h ), 1 . 71 ( br t , j = 13 . 7 hz , 2h ). analysis calculated for c 27 h 24 fno 4 : c , 72 . 80 ; h , 5 . 43 ; n , 3 . 13 . found : c , 72 . 83 ; h , 5 . 82 ; n , 2 . 82 . to a slurry of 7 - benzyloxy - 3 -[ 4 -( 4 - fluorophenyl )- 4 - hydroxy - piperidine - 1 - yl ]- chromenone ( 8 . 24 g , 18 . 5 mmol ) in ethanol ( 400 ml ) and tetrahydrofuran ( 600 ml ) was added sodium borohydride ( 7 . 0 g , 185 mmol ). the mixture was stirred overnight . additional sodium borohydride ( 7 . 0 g ) was added and the reaction mixture was stirred for 3 days . water was added and the solvent was removed at reduced pressure at 45 ° c . the solids which formed were collected and washed well with water and then ether . the solid was further dried in vacuo overnight to give 5 . 01 g , 60 % of 3r * 4s * 7 - benzyloxy - 3 -[ 4 -( 4 - fluorophenyl )- 4 - hydroxy - piperidin - 1 - yl ]- chroman - 4 - ol which was suitable for use without further purification . a sample recrystallized from ethyl acetate / chloroform had mp . 194 - 195 ° c . ; nmr δ7 . 56 - 7 . 30 ( m , 8h ), 7 . 06 ( long range coupled t , j = 8 . 7 hz , 2h ) 6 . 63 ( dd , j = 2 . 4 , 8 . 5 hz , 1h ), 6 . 47 ( d , j = 2 . 4 hz , 1h ), 5 . 04 ( s , 2h ), 4 . 77 ( d , j = 4 . 5hz , 1h ), 4 . 37 ( dd , j = 3 . 5 , 10 . 4hz , 1h ), 4 . 13 ( t , j = 10 . 4 hz , 1h ), 3 . 82 ( brs , 1h ), 3 . 11 ( br d , j = 11 . 2 hz , 1h ), 2 . 92 - 2 . 71 ( m , 4h ), 2 . 21 - 2 . 06 ( m , 2h ), 1 . 87 - 1 . 73 ( m , 2h ), 1 . 54 ( s , 1h ). analysis calculated for c 27 h 28 fno 4 : c , 72 . 14 ; h , 6 . 28 ; n , 3 . 12 . found c , 72 . 15 ; h , 6 . 21 ; n , 3 . 12 . a mixture of 3r * 4s * 7 - benzyloxy - 3 -[ 4 -( 4 - fluorophenyl )- 4 - hydroxy - piperidin - 1 - yl ]- chroman - 4 - ol ( 0 . 80 g , 1 . 78 mmol ), 10 % palladium on carbon ( 0 . 16 g ), methanol ( 40 ml ), and acetic acid ( 0 . 8 ml ) was hydrogenated for 8 hours with a starting pressure of 48 . 5 psi . the reaction was filtered through celite and the filtrate was concentrated . the residue was stirred vigorously with ether and saturaturated sodium bicarbonate for 1 hour . the solid was washed with water and ether and dried in vacuo . recrystallization from ethanol yielded 0 . 35 g ( 54 %) of 3r * 4s * 3 -[ 4 -( 4 - fluorophenyl )- 4 - hydroxy - piperidin - 1 - yl ]- chroman - 4 , 7 - diol as a white solid which had mp 159 - 160 ° c . ; nmr dmso ∂ σ δ7 . 55 - 7 . 47 ( m , 2h ), 7 . 11 ( t , j = 9 hz , 2h ), 7 . 02 ( d , j = 8 . 4 hz , 1h ) k , 6 . 32 ( dd , j = 2 . 3 , 8 . 3 hz , 1h ), 6 . 15 ( d , j = 2 . 3 hz 1h ), 5 . 10 - 4 . 50 ( br m with s at 4 . 63 , 3h ), 4 . 23 ( dd , j = 2 . 8 , 10 . 3 hz , 1h ), 4 . 04 ( t , j = 10 . 5 hz , 1h ), 2 . 99 ( br d , j = 10 . 8 hz , 1h ), 2 . 86 ( br d , j = 10 . 7 hz , 1h ), 2 . 73 - 2 . 50 ( m , 3h ), 2 . 08 - 1 . 90 ( m , 2h ), 1 . 58 ( br d , j = 13 hz , 2h ). analysis calculated for c 2 h 22 fno 4 . 0 . 25h 2 o ; c , 66 . 01 ; h , 6 . 23 ; n , 3 . 85 . found : c , 66 . 22 ; h , 6 . 58 ; n . 3 . 46 .
the invention provides new methods for treating certain disorders resulting from neurodegeneration and for treating depression which comprise administration of nr2b subunit selective nmda antagonists . the disorders that can be treating by the invention include hearing loss , vision loss , neurodegeneration caused by epileptic seizures , neurotoxin poisoning , restless leg syndrome , multi - system atrophy , non - vascular headache , and depression .