this invention provides novel pharmaceutically useful optically active organic carbamate compounds represented by the structural formulas ( i ) and ( ii ), wherein the phenyl ring is substituted at x with one to five halogen atoms selected from fluorine , chlorine , bromine or iodine atoms , and r 1 , r 2 , r 3 , r 4 , r 5 and r 6 is a functional group selected from hydrogen and straight or branched alkyl groups with one to four carbons optionally substituted with a phenyl group with substituents selected from the group consisting of hydrogen , halogen , alkyl , alkyloxy , amino , nitro and cyano . the compounds of the present invention possess selective pharmacological properties and are useful in treating and preventing central nervous system disorders including convulsions , epilepsy , stroke and muscle spasm . it will be apparent to those skilled in the art that the compounds of the present invention contain chiral centers . the compounds of formula ( i ) and ( ii ) contain an asymmetric carbon atom at the benzylic position , which is the aliphatic carbon adjacent to the phenyl ring . the therapeutic properties of the compounds may to a greater or lesser 5 degree depend on the stereochemistry of a particular compound . the scope of the present invention includes pure enantiomeric forms and enantiomeric mixtures wherein one of the enantiomers predominates the compounds represented by the structural formulas ( i ) and ( ii ). preferably , one of the enantiomers predominates to the extent of about 90 % or greater , and most preferably , about 98 % or greater . the carbamate compounds represented by the structural formula ( i ) may be prepared by the synthetic method described in scheme 1 , a detailed description of which follows . a 2 - phenyl - 1 , 2 - ethanediol with halogen substituent on the phenyl ring is reacted with dimethyl carbonate in the presence of catalytic amount of sodium methoxide . the by - product methanol is removed by a vacuum distillation and the residual product is dried in vacuo . the crude reaction product is subsequently dissolved in a lower alkanol , such as methanol , and an excess amount of an amine is added to the reaction solution at room temperature to provide two regioisomeric forms of a monocarbamate of 2 - phenyl - 1 , 2 - ethanediol with a halogen substituent on the phenyl ring . regioisomeric forms of monocarbamates of 2 - phenyl - 1 , 2 - ethanediol with a halogen substituent on the phenyl ring are separated by flash column chromatography providing the desired compound as the major product . in the structural formula ( i ) in scheme 1 , the phenyl ring is substituted at x with from one to five halogen atoms selected from fluorine , chlorine , bromine or iodine atoms , and r 1 and r 2 are functional groups selected from hydrogen and straight or branched alkyl with one to four carbons optionally substituted with a phenyl group with substituents selected from the group consisting of hydrogen , halogen , alkyl , alkyloxy , amino , nitro and cyano . the carbamate compounds represented by the structural formula ( ii ) may be prepared by the synthetic method described either in scheme 2 , in scheme 3 or in scheme 4 , the detailed descriptions of which follow . when r 3 , r 4 , r 5 and r6 are hydrogen , the desired dicarbamate compound is prepared by the synthetic method described in scheme 2 . a 2 - phenyl - 1 , 2 - ethanediol with halogen substitutent on the phenyl ring is dissolved in a solvent selected from the group consisting of acetonitrile , tetrahydrofuran and dichloromethane , and is treated with excess sodium cyanate . the resulting mixture is cooled in an ice - bath , and excess methanesulfonic acid is added slowly . when the starting diol is not detected by thin layer chromatography , the reaction mixture is neutralized with aqueous sodium hydroxide and extracted with methylene chloride . the organic extract is dried , filtered , concentrated and the desired compound is purified by flash column chromatography . in structural formula ( ii ) in scheme 2 , the phenyl ring is substituted at x with from one to five halogen atoms selected from fluorine , chlorine , bromine or iodine atoms . when the carbamate units in a dicarbamate represented by structural formula ( ii ) are identical , that is when r 3 = r 5 and r 4 = r 6 , the desired compound is prepared by synthetic method described in scheme 3 . a 2 - phenyl - 1 - 2 - ethanediol with halogen substituent on the phenyl ring is dissolved in dichloromethane and is treated with about 2 equivalents of carbonyl diimidazoie . the resulting mixture is stirred until the starting material is not observed by thin layer chromatography analysis , and the mixture is treated with excess amount of amine ( r 3 r 4 nh ). it takes typically more than 24 hours to complete the reaction . after a routine aqueous wash , the crude reaction product is purified by flash column chromatography to provide the desired product . in structural formula ( ii ) in scheme 3 , the phenyl ring is substituted at x with from one to five halogen atoms selected from fluorine , chlorine , bromine or iodine atoms , and r 3 and r 4 may be a functional group selected from hydrogen and straight or branched alkyl with one to four carbons optionally substituted with a phenyl group with substituents selected from the group consisting of hydrogen , halogen , alkyl , alkyloxy , amino , nitro and cyano . when the carbamate units in a dicarbamate represented by the structural formula ( ii ) are different , the desired compound is prepared from a corresponding monocarbamate represented by the structural formula ( i ) which was prepared by the synthetic method described in scheme 1 , using the synthetic method described in scheme 4 . a 2 - phenyl - 1 , 2 - ethanediol monocarbamate from a group of compounds represented by the structural formula ( i ) is treated with about 1 equivalent of carbonyl diimidazole . the resulting mixture is stirred until the starting material is not observed by thin layer chromatography analysis , and the mixture is treated with an excess amount of amine ( r 5 r 6 nh ). it takes typically more than 24 hours to complete the reaction . after a routine aqueous wash , the crude reaction product is purified by flash column chromatography to provide the desired product . in structural formula ( ii ) in scheme 4 , the phenyl ring is substituted at x with from one to five halogen atoms selected from fluorine , chlorine , bromine or iodine atoms , and each of r 1 , r 2 , r 5 and r 6 is a functional group selected from hydrogen and straight or branched alkyl with one to four carbons optionally substituted with phenyl group with substituents selected from the group_consisting of hydrogen , halogen , alkyl , alkyloxy , amino , nitro and cyano . in utilizing the compounds of the present invention for the treatment of diseases of the central nervous system , particularly the treatment of convulsions , epilepsy , stroke and muscle spasm , it is preferred to administer the compounds orally . since the compounds are well absorbed orally , it usually will not be necessary to resort to parenteral administration . for oral administration , the present carbamate compounds are preferably combined with a pharmaceutical carrier . the ratio of the carrier to the compounds of the present invention is not critical to achieve the effects of the medicine on the central nervous system , and they can vary considerably , depending on whether the composition is to be filled into capsules or formed into tablets . in tableting , it is usually desirable to employ at least as much pharmaceutical carrier as the pharmaceutically active ingredients . various edible pharmaceutical carriers or mixtures thereof can be used . suitable carriers , for example , are a mixture of lactose , dibasic calcium phosphate and corn starch . other pharmaceutically acceptable ingredients can be further added , including lubricants such as magnesium stearate . the therapeutic use of the compounds claimed in the present invention as anticonvulsants has been proven by the “ maximal electroshock ( mes )” test , which is a well - established pharmacological screening method for anticonvulsants against partial seizures , and the results are presented in table 1 . the procedure employed in the mes test for anticonvulsants follows . the compound dosing , solutions were prepared in saline , and the subject , namely , mice ( cf - 1 strain ), were dosed orally . after the designated number of hours , maximal electroshock was induced in mice via corneal electrodes using iitc life science model 11a shocker at 50 ma - 60 hz for 0 , 2 second . upon inducing , maximal electroshock , the elimination of hindlimb tonic extension was considered as providing evidence of the protection by an anticonvulsant . median efficacy dose ( ed50 ) levels were determined using three different dose levels with at least 6 mice in each group . compounds with smaller ed50 value are more potent as anticonvulsants . table i ed50 entry x *( chiralty ) y z ( mg / kg ) hour 1 o - cl rac . h conh 2 33 . 7 1 2 o - cl s h conh 2 13 . 0 1 3 o - cl r h conh 2 50 . 0 1 4 2 , 6 - cl 2 s h conh 2 9 . 4 1 5 o - cl rac . conh 2 conh 2 25 1 6 o - cl r conh 2 conh 2 16 . 0 1 7 o - cl s conh 2 conh 2 22 . 0 1 8 p - cl rac . conh 2 conh 2 29 . 1 1 9 p - cl r conh 2 conh 2 26 . 2 1 10 p - cl s conh 2 conh 2 21 . 5 4 11 2 , 6 - cl 2 rac . conh 2 conh 2 7 . 4 1 12 2 , 6 - cl 2 r conh 2 conh 2 10 . 7 1 13 o - cl r conh 2 conhch 3 8 . 9 4 14 o - cl r conhch 3 conhch 3 & gt ; 20 4 15 o - cl r conhipr conhipr ≈ 10 ( ip ) 1 16 o - cl r conhph conhph & gt ; 20 4 17 o - cl r conhch 2 ph conhch 2 ph & gt ; 20 4 a better understanding of the present invention may be obtained in light of following examples which are set forth to illustrate , but are not to be construed to limit , the present invention . the diols used in the syntheses of carbamate compounds were prepared by a dihydroxylation reaction from their corresponding styrenic compound . in preparations of optically active diols , sharpless &# 39 ; s asymmetric dihydroxylation catalysts were used . general procedure for preparing unsubstituted dicarbamate compounds ( dl )- 1 - o - chlorophenyl - 1 , 2 - ethanediol was dissolved in tetrahydrofaran ( 115 ml ) and sodium cyanate ( 9 . 0 g ) and methanesulfonic acid ( 9 . 5 ml ) was added in an ice bath . the resulting reaction mixture was stirred for 18 hours , extracted with tetrahydrofuran dichloro - methane mixture , washed with 5 % aqueous sodium hydroxide , dried over sodium sulfate , filtered , concentrated and purified by flash column chromatography to yield a white solid . analytically pure ( dl )-( 2 -( 2 - chlorophenyl )- 2 - carbamoyloxyethyl ) oxocarboxamide ( m . p . 190 ° c .) was obtained after recrystallization from ethanol - ether mixture . ( r )-( 2 -( 2 - chlorophenyl )- 2 - carbamoyloxyethyl ) oxocarboxamide ( 2 . 1 g , yield 46 %, m . p . 172 - 174 ° c ., [ α ] d = 84 . 9 ( c = 2 . 70 , dmf )) was prepared using the same synthetic method described in example 1 , except that ( r )- 1 - o - chlorophenyl - 1 , 2 - ethanediol ( 3 . 0 g ) was used instead of ( d / l )- 1 - o - chlorophenyl - 1 , 2 - ethanediol . ( s )-( 2 -( 2 - chlorophenyl )- 2 - carbamoyloxyethyl ) oxocarboxamide ( 1 . 6 g , yield 35 %, m . p . 167 - 169 ° c ., [ α ] d =− 84 . 1 ( c = 2 . 27 , dmf )) was prepared using the same synthetic method described in example 1 , except that ( s )- 1 - o - chlorophenyl - 1 , 2 - ethanediol was used instead of ( d / l )- 1 - o - chlorophenyl - 1 , 2 - ethanediol . ( dl )-( 2 -( 3 - chlorophenyl )- 2 - carbamoyloxyethyl ) oxocarboxamide ( 2 . 41 g , yield 80 %, m . p . 188 - 190 ° c .) was prepared using the same synthetic method described in example 1 , except that ( dl )- 1 - m - chlorophenyl - 1 , 2 - ethanediol was used instead of ( dl )- 1 - o - chlorophenyl - 1 , 2 - ethanediol . ( dl )-( 2 -( 4 - chlorophenyl )- 2 - carbamoyloxyethyl ) oxocarboxamide ( 1 . 97 g , yield 38 %, m . p . 146 - 148 ° c .) was prepared using the same synthetic method described in example 1 , except that ( dl )- 1 - p - chlorophenyl - 1 , 2 - ethanediol was used instead of ( dl )- 1 - o - chlorophenyl - 1 , 2 - ethanediol . ( r )-( 2 -( 4 - chlorophenyl )- 2 - carbamoyloxyethyl ) oxocarboxamide ( 2 . 53 g , yield 84 %, m . p . 178 - 180 ° c ., [ α ] d =− 24 . 38 ( c = 2 . 60 , meoh )) was prepared using the same synthetic method described in example 1 , except that ( r )- 1 - p - chlorophenyl - 1 , 2 - ethanediol was used instead of ( dl )- 1 - o - chlorophenyl - 1 , 2 - ethanediol . ( s )-( 2 -( 4 - chlorophenyl )- 2 - carbamoyloxyethyl ) oxocarboxamide ( 2 . 04 g , yield 68 %, m . p . 177 - 179 ° c ., [ α ] d = 25 . 56 ( c = 2 . 75 , meoh )) was prepared using the same synthetic method described in example 1 , except that ( s )- 1 - p - chlorophenyl - 1 , 2 - ethanediol was used instead of ( dl )- 1 - o - chlorophenyl - 1 , 2 - ethanediol . ( dl )-( 2 -( 2 , 6 - dichlorophenyl )- 2 - carbamoyloxyethyl ) oxocarboxamide ( 1 . 71 . g , yield 40 %, m . p . 160 - 162 ° c .) was prepared using the same synthetic method described in example 1 , except that ( dl )- 1 -( 2 , 6 - dichlorophenyl )- 1 , 2 - ethanediol was used instead of ( dl )- 1 - o - chlorophenyl - 1 , 2 - ethanediol . ( r )-( 2 -( 2 , 6 - dichlorophenyl )- 2 - carbamoyloxyethyl ) oxocarboxamide ( 7 . 40 g , yield 52 %, m . p . ° c ., [ α ] d = 36 . 01 ( c = 2 . 58 , meoh ) was prepared using the same synthetic method described in example 1 , except that ( r )- 1 -( 2 , 6 - dichlorophenyl )- 1 , 2 - ethanediol was used instead of ( dl )- 1 , 2 - ethanediol . 1 , 1 ′- carbonyldiimidazole ( 1 . 0 g , 6 . 12 mmol ) was added to a solution of ( r )-( 2 -( 2 - chlorophenyl )- 2 - hydroxyethyl ) oxocarboxamide ( 1 . 2 g , 5 . 56 mmol ) in tetrahydrofuran ( 4 ml ) at 5 ° c . the reaction mixture was allowed to come to room temperature and stirred 45 min . methylamine ( 5 . 6 ml of a 2m solution in thf ) was added at 5 ° c . the reaction mixture was stirred for 18 hr at room temperature , extracted with ethyl acetate , washed with 0 . 5 aquous hydrochloric acid , saturated sodium bicarbonate and brine . the extracts were dried over sodium sulfate , filtered , concentrated and purified by flash chromatography to yield a white solid ( r )-( 2 -( 2 - chlorophenyl )- 2 - n - carbamoyloxyethyl ) oxocarboxamide . ( 1 . 4 g , yield 93 %, m . p . 128 - 130 ° c ., [ α ] d = 0 . 937 ( c = 2 . 49 , meoh ) ( r )-( 2 -( 2 - chlorophenyl )- 2 - n - isopropylcarbamoyloxyethyl )- oxocarboxamide ( 1 . 0 g , yield 62 %, m . p . 163 - 165 ° c ., [ α ],) d = 3 99 ( c = 2 . 10 , meoh ) was prepared using the same synthetic method described in example 10 , except that isopropylamine was used instead of methylamine . ( r )-( 2 -( 2 - chlorophenyl )- 2 - n - cyclopropylcarbamoyloxyethyl )- oxocarboxamide ( 1 . 60 , yield 96 %, m . p . 111 - 113 ° c ., [ α ] d ,= 2 . 39 ( c = 2 . 25 , meoh ) was prepared using the same synthetic method described in example 10 , except that cyclopropylamine was used instead of methylamine . a solution of ( r )-( 2 - chlorophenyl )- 1 , 2 - ethanediol ( 2 . 0 g , 11 . 6 mmol ) in tetrahydrofuran was added dropwise to a suspension of 1 , 1 ′- carbonyldiimidazole ( 4 . 13 g , 25 . 5 mmol ) in tetrahydrofuran ( 10 ml ) at 5 ° c . over a 20 min period . after stirring 1 hr at room temperature , methylamine ( 23 . 2 ml 2m solution in thf , 46 . 4 mmol ) was added at 5 ° c . after stirring 18 hr at room temperature , the reaction mixture was concentrated in vacuuo and purified by flash chromatography to give a white solid ( 2 . 03 g , 61 %, m . p . 152 - 154 ) ( r )- n - isopropyl ( 2 -( 2 - chlorophenyl )- 2 -( n - isopropylcarbamoyloxyethyl )- oxocarboxamide ( 3 . 50 g , yield 88 %, m . p . 151 - 153 ° c .,[ α ] d = 1 . 33 ( c = 2 . 63 , meoh ) was prepared using the same synthetic method described in example 13 , except that isopropylamine was used instead of methylamine . ( r )- n - phenyl ( 2 -( 2 - chlorophenyl )- 2 - n - phenylcarbamoyloxyethyl )- oxocarboxamide ( 2 . 74 g , yield 57 %, m . p . 46 - 48 ° c .) was prepared using the same synthetic method described in example 13 , except that analine was used instead of methylamine . ( r )- n - benzyl ( 2 -( 2 - chlorophenyl )- 2 -( n - benzylcarbamoyloxyethyl )- oxocarboxamide ( 2 . 88 g , yield 76 %, m . p . 80 - 82 ° c .) was prepared using the same synthetic method described in example 13 , except that benzylamine was used instead of methylamine . in a 50 ml round bottom flask equipped with vacuum distillation apparatus , ( dl )- o - chlorophenyl - 1 , 2 - ethanediol ( 10 . 98 g ), diethyl carbonate ( 10 . 25 ml ) and sodium methoxide ( 305 mg ) were placed and the resulting mixture was heated in an oil bath up to 135 ° c . with magnetic stirring . the by - product ethyl alcohol was collected in a receiver flask . after collecting approximately 10 ml of ethanol , the residual ethyl alcohol remaining in the reaction mixture was removed by vacuum distillation . the reaction mixture was cooled to room temperature , dissolved in dichloromethane ( 40 ml ), washed with brine ( 15 ml ), dried over anhydrous sodium sulfate , filtered and then concentrated in vacuo to produce ( dl )- 1 - o - chlorophenyl - 1 , 2 - ethanediol carbonate ( 12 . 58 g , yield 100 %). in a 200 ml round bottom flask equipped with a magnetic stirrer , approximately 12 ml of liquid ammonia was condensed at − 78 ° c ., and ( dl )- 1 - o - chlorophenyl - 1 , 2 - ethanediol carbonate ( 6 . 0 g ) in methanol ( 200 ml ) was added slowly . the reaction mixture was slowly warmed to room temperature and was stirred at room temperature for another hour , and then concentrated in vacuo . ( dl )-( 2 -( 2 - chlorophenyl )- 2 - hydroxyethyl )- oxocarboxamide ( 1 . 97 g , yield 30 %, m . p . 100 ° c .) was obtained after a chromatographic purification . ( r )-( 2 -( 2 - chlorophenyl )- 2 - hydroxyethyl ) oxocarboxamide ( 3 . 35 g , yield 45 %, m . p . 133 ° c ., [ α ] d =− 63 . 9 ( c = 2 . 22 , methanol )) was prepared using the same synthetic method described in example 17 , except that ( r )- o - chlorophenyl - 1 , 2 - ethanediol was used instead of ( dl )- 1 - o - chlorophenyl - 1 , 2 - ethanediol . ( s )-( 2 -( 2 - chlorophenyl )- 2 - hydroxyethyl ) oxocarboxamide ( 3 . 89 g , yield 52 %, m . p . 133 ° c ., [ α ] d = 64 . 9 ( c = 2 . 69 , methanol )) was prepared using the same synthetic method described in example 17 , except that ( s )- o - chlorophenyl - 1 , 2 - ethanediol was used instead of ( dl )- 1 - o - chlorophenyl - 1 , 2 - ethanediol . ( dl )- 1 - m - chlorophenyl - 1 , 2 - ethanediol carbonate was prepared using the same synthetic method described in example 17 , except that ( dl )- 1 - m - chlorophenyl - 1 , 2 - ethanediol was used instead of ( dl )- 1 - o - chlorophenyl - 1 , 2 - ethanediol in a quantitative yield . in a 250 ml round bottom flask equipped with a magnetic stirrer , ( dl )- 1 - m - chlorophenyl - 1 , 2 - ethanediol carbonate ( 10 . 95 g ) was dissolved in methanol ( 60 ml ) and the mixture was cooled in an ice bath . ammonium hydroxide ( 30 ml , 28 - 30 %) was added to the mixture and the mixture was stirred at room temperature for 1 hour or until the reaction was completed as evidenced by thin layer chromatography . excess ammonium hydroxide and methanol were removed in vacuo to yield a white solid . ( dl )-( 2 ( 3 - chlorophenyl )- 2 - hydroxyethyl ) oxocarboxamide ( 1 , 25 g , yield 10 %, m . p . 90 ° c .) was purified by flash column chromatography . ( r )-( 2 -( 3 - chlorophenyl )- 2 - carbamoyloxyethyl ) oxocarboxamide ( 1 . 77 g , 45 %, m . p . 114 - 116 ° c .) was prepared using the same synthetic method described in example 20 , except ( r )- 1 - m - chlorophenyl - 1 , 2 - ethanediol was used instead of ( dl )- 1 - m - chlorophenyl - 1 , 2 - ethanediol . ( s )-( 2 -( 3 - chlorophenyl )- 2 - carbamoyloxyethyl ) oxocarboxamide ( 1 - 36 g , yield 25 %, m . p . 117 - 119 ° c ., [ α ] d = 12 . 88 ( c = 2 . 30 , meoh ) was prepared using the same synthetic method described in example 20 , except ( s )- 1 - m - chlorophenyl - 1 , 2 - ethanediol was used instead of ( dl )- 1 - m - chlorophenyl - 1 , 2 - ethanediol was used instead of ( dl )- 1 - m - chlorophenyl - 1 , 2 - ethanediol . ( r )( 2 -( 4 - chlorophenyl )- 2 - hydroxyethyl ) oxocarboxamide ( 1 - 15 - g , yield 31 %, m . p . 110 - 112 ° c .) was prepared using the same synthetic method described in example 20 , except ( r )- 1 - p - chlorophenyl - 1 , 2 - ethanediol was used instead of ( dl )- 1 - m - chlorophenyl - 1 , 2 - ethanediol . ( s )-( 2 -( 4 - chlorophenyl )- 2 - hydroxyethyl ) oxocarboxamide ( 1 . 14 g , yield 30 %, m . p . 110 - 112 ° c ., [ α ] d 18 . 62 ( c = 2 . 40 , meoh ) was prepared using the same synthetic method described in example 20 , except ( s )- 1 - p - chlorophenyl - 1 , 2 - ethanediol was used instead of ( dl )- 1 - m - chlorophenyl - 1 , 2 - ethanediol . ( dl )-( 2 -( 2 , 6 - dichlorophenyl )- 2 - hydroxyethyl ) oxocarboxamide ( 1 . 05 g , yield 43 %, m . p . 120 - 122 ° c .) was prepared using the same synthetic method described in example except ( dl )- 2 -( 2 , 6 - dichlorophenyl )- 1 , 2 - ethanediol was used instead of ( dl )- 1 - m - chlorophenyl - 1 , 2 - ethanediol .
enantiomeric forms of monocarbamates of halogenated 2 - pheny - 1 , 2 - ethanediol and dicarbamates of halogenated 2 - pheny - 1 , 2 - ethanediol have been found to be effective in the treatment of disorders of the central nervous system , especially as anti - convulsive or anti - epileptic agents .