a series of new n - substituted derivatives of morphinan were synthesized , and their binding affinity for three opioid receptors ( i . e ., μ , δ , and κ ) was determined . a paradoxical effect of n - propargyl ( mcl - 117 ) and n -( 3 - iodoprop -( 2e )- enyl ) ( mcl - 118 ) substituents on the binding affinities for the μ and κ opioid receptors was observed . all of these novel derivatives showed a preference for the μ and κ versus δ binding . to systematically study the effects of n - substituents in the morphinan nucleus on binding affinity , selectivity , and efficacy at μ and κ opioid receptors , a variety of substituents were introduced on the nitrogen atom in morphinan , and then the new derivatives were assayed for biological activity . the κ / δ selectivity of most of these derivatives was considerably better than that of levorphanol and ethylketocyclazocine ( ekc ). the target derivatives 3 - 13 and 20 - 31 , shown in fig1 were synthesized from norlevorphanol 2 by one of the three methods as depicted in fig2 . demethylation of levorphanol 1 was accomplished according to the procedure reported by degraw and engstrom ( j . labelled compd . 11 : 233 , 1975 ). thus , levorphanol was treated with ethyl chloroformate in refluxing chloroform in the presence of k 2 co 3 followed by partial hydrolysis of the product with 10 % naoh in methanol . norlevorphanol 2 was obtained in good yield after hydrolysis of the resulting carbamate ( structure not shown ) intermediate in a mixture of hydrochloric acid and glacial acetic acid . direct alkylation of norlevorphanol with various alkyl halides in dimethyl formamide ( dmf ) using k 2 co 3 or nahco 3 as a base provided n - substituted derivatives 3 - 13 in good to excellent yields ( all final compounds were characterized by nmr and mass spectroscopy , and gave satisfactory c , h , and n analyses , i . e ., within + 0 . 4 % of theoretical values ). in an alternative procedure , acylation of norlevorphanol with acid chlorides followed by reduction of the intermediate amide 14 - 19 with lialh 4 in tetrahydrofuran ( thf ) afforded the tertiary amines 20 - 25 . alkylation of norlevorphanol with 1 - aryl - 3 -( dimethylamino )- 1 - propanone methiodide in dmf in the presence of na 2 co 3 yielded ketones 26 - 28 , which were then reduced with nabh 4 to afford the alcohols 29 - 31 as a mixture of hydroxy diastereomers . the n -( 3 - iodoprop -( 2e )- enyl ) and n -( 3 - iodoprop -( 2z )- enyl ) derivatives 34 and 35 were obtained by iododestannylation of compounds 32 and 33 by treatment with iodine in chloroform . the reaction scheme is shown in fig3 . the tributyltin precursors 32 and 33 were prepared by hydrostannylation of the n - propargyl derivative 9 with hsnbu 3 in the presence of et 3 b as catalyst followed by column separation of the two isomers ( see goodman et al ., j . med . chem ., 37 : 1535 , 1994 ). another efficient route to the ( e )- tributyltin precursor 32 involved alkylation of norlevorphanol with 3 -( tributylstannyl ) prop -( 2e )- enyl chloride , which was prepared by chlorination of 3 -( tributylstannyl ) prop -( 2e )- en - 1 - ol with pph 3 and ccl 4 . the ( e )- stannyl alcohol was obtained by hydrostannylation of propargyl alcohol using the literature procedure of emond et al ., j . med . chem ., 40 : 1366 ( 1997 ). the structures and physical properties of these new n - substituted derivatives are shown in fig1 . the binding affinities of compounds 3 - 13 , 20 - 24 , 26 - 31 , 34 , and 35 for the μ , δ , and κ opioid receptors were assessed using competitive binding assays in guinea pig brain membranes employing [ 3 h ] damgo ( μ agonist ), [ 3 h ] naltrindole ( δ antagonist ) and [ 3 h ] u69 , 593 ( κ agonist ) as radioligands , using the methods described in neumeyer et al ., j . med . chem ., 43 : 114 ( 2000 ). the results are summarized in fig4 . for comparison purposes , the binding data for u50 , 488 , mr2033 , ekc , levorphanol , and cyclorphan are also included in fig4 . antinociceptive biological data can also be obtained using the tail - flick and / or mouse writhing tests ( id .). the n - substituent has a significant effect on both the opioid receptor binding affinity and selectivity of these morphinan derivatives . for example , our previous research indicated that replacement of the methyl group in levorphanol with a cyclopropylmethyl group can greatly increase affinity at the δ and κ opioid receptors ( 20 - fold and 40 - fold , respectively ), while the affinity at the μ opioid receptor increases just 2 - fold ( id .). the n - cyclobutylmethyl analog mcl - 101 showed 30 - fold increase in binding affinity at the κ opioid receptor , but the increase for the μ and δ opioid receptors was less pronounced ( 2 - fold and 3 - fold , respectively ). mcl - 101 possessed almost the same affinity for the μ and κ opioid receptors as cyclorphan , but mcl - 101 had greater κ / δ selectivity ( 18 - fold vs 4 - fold ). further increasing the size of the ring led to a loss in binding affinity . consistent with this observation , the n - cyclohexylmethyl derivative 21 ( mcl - 105 ) displays very low affinity for the three opioid receptors . surprisingly , the n - propargyl derivative 9 ( mcl - 117 ) and the n -( 3 - iodoprop -( 2e )- enyl ) derivative 34 ( mcl - 118 ) exhibited unexpectedly high affinity for the μ and κ opioid receptors with k i values in the picomolar range . in fact , these two compounds are among the most potent ligands for the μ and κ opioid receptors identified to date . compounds 9 and 34 had the same high affinity for the μ opioid receptor , but 34 displayed 10 - fold decreased affinity for the κ and 43 - fold decreased affinity for the δ opioid receptor in comparison to compound 9 . the n -( 3 - iodoprop -( 2z )- enyl ) derivative 35 , however , displayed dramatically decreased ( 100 - fold and 17 - fold ) affinity for the μ and κ receptors relative to 34 . the n - isopropyl derivative 4 ( mcl - 108 ) showed much higher ( 14 - fold ) affinity for the κ receptor but lower ( 2 - fold ) affinity for the μ receptor than levorphanol . replacement of the methyl with an allyl group 8 ( mcl - 113 , levallorphan ) resulted in 15 - fold increase in affinity for the κ opioid receptor and almost no changes in affinity for both of the δ and μ opioid receptors . the n -( 3 - fluoropropyl ) derivative 3 ( mcl - 107 ) also displayed very high affinity for all three opioid receptors ( k i = 0 . 18 nm , 0 . 85 nm , and 0 . 083 nm for the μ , δ , and κ receptor , respectively ). the n - methoxyethyl derivative δ ( mcl - 110 ) was found to have high affinity for the κ and μ opioid receptors ( k i = 0 . 094 nm and 0 . 11 nm , respectively ). replacement of methoxyethyl with ethoxyethyl resulted in a 2 - fold and 4 - fold loss in affinity for the μ and κ opioid receptors , respectively . the n - phenoxyethyl derivative 13 ( mcl - 127 ) exhibited decreased affinity for all three opioid receptors relative to the methoxyethyl derivative 6 . without intending to be bound by any theory , it appears that the size of the ether chain affects the affinity for the three opioid receptors . the n - methoxymethyl and n - fluoropropyl derivatives of normetazocine were found to bind nonselectively , with high affinity for the μ and κ receptors . the n - furanylmethyl derivative 22 ( mcl - 119 ) displayed high affinity for the μ and κ receptors ( k i = 0 . 54 nm and 0 . 13 nm , respectively ). replacement of the furanylmethyl group with thienylmethyl resulted in decreased affinity for all three opioid receptors , but this decrease was most pronounced for the δ opioid receptor ( 6 - fold vs . 2 - fold ). thus , the n - thienylmethyl derivative 23 ( mcl - 120 ) displayed good selectivity for the μ and κ receptors versus δ receptor ( κ / δ = 160 , μ / δ = 14 ). the n - benzyl derivative 7 ( mcl - 111 ) showed dramatically decreased affinity at all three opioid receptors relative to 22 and 23 . adding one more methylene unit between the nitrogen and the phenyl ring ( i . e ., the phenethyl derivative 24 ) led to a great increase in binding affinity . the increase is 130 - fold and 16 - fold for the δ and μ opioid receptors , respectively . the n - cyanoethyl derivative 11 ( mcl - 125 ) displayed increased affinity ( 10 - fold ) for the κ opioid receptor as compared with levorphanol ( the n - methyl derivative ). replacement of the 2 - cyanoethyl with a 3 - cyanopropyl group caused few changes in binding affinity for all three opioid receptors . however , the n - trifluoropropyl derivative 12 had decreased affinity for the μ and δ receptors and similar affinity for the κ receptor relative to levorphanol . the three mannich base derivatives 26 - 28 showed similar binding profiles with good affinity for the μ opioid receptor and low affinity for both the κ and δ opioid receptors . reduction of the keto group to secondary alcohol resulted in loss in binding affinity for the three opioid receptors . again without wishing to be bound by any theories , it seems that a hydroxyl group in the n - substituent interferes with the interaction of the ligand with the opioid receptors , probably due to the hydroxyl group &# 39 ; s hydrogen - donating property . in conclusion , the n - substituent of morphinan had significant effect on the binding affinity and selectivity for the three opioid receptors . these n - substituted derivatives exhibited a strong preference for μ and κ versus δ binding . the n -( 3 - fluoropropyl ) 3 ( mcl - 107 ), n - methoxyethyl 6 ( mcl - 110 ), the n - propargyl 9 ( mcl - 117 ), and the n -( 3 - iodoprop -( 2e )- enyl ) 34 ( mcl - 118 ) derivatives possessed high affinity for the μ and κ opioid receptors . in particular , the n - propargyl analogue 9 ( mcl - 117 ) and the n -( 3 - iodoprop -( 2e )- enyl ) analog 34 ( mcl - 118 ) showed very high affinity for the μ and κ opioid receptors with k i values in the picomolar range . as noted above , the new compounds can be assayed for in vivo activity using , for example , the tail flick assay as described by neumeyer et al . ( j . med . chem ., 43 : 114 - 122 , 2000 ) and mclaughlin et al . ( j . pharmacol . exp . ther ., 289 : 304 - 311 , 1999 ), and / or the acetic acid writhing test described by neumeyer et al . ( j . med . chem ., 43 : 114 - 122 , 2000 ) and xu et al . ( j . pharmacol . exp . ther ., 279 : 539 - 547 , 1996 ). the new compounds for use in accordance with the present invention can be formulated in a conventional manner using one or more physiologically acceptable carriers or excipients . agents used in the formulations and their physiologically acceptable salts and solvates can be prepared for administration by various methods . for example , administration can be parenteral , e . g ., intravenous , subcutaneous , intramuscular , intracranial , intraorbital , ophthalmic , intraventricular , intracapsular , intraspinal , intracistemal , intraperitoneal , transmucosal ; or administration can be oral . the compounds can be formulated in various ways , according to the route of administration . for oral administration , the formulations can take the form of , for example , tablets or capsules prepared by conventional means with pharmaceutically acceptable excipients such as binding agents ( for example , pregelatinised maize starch , polyvinylpyrrolidone or hydroxypropyl methylcellulose ); fillers ( for example , lactose , microcrystalline cellulose or calcium hydrogen phosphate ); lubricants ( for example , magnesium stearate , talc or silica ); disintegrants ( for example , potato starch or sodium starch glycolate ); or wetting agents ( for example , sodium lauryl sulphate ). the tablets can be coated or encapsulated ( such as in a coating of hard gelatin or cyclodextran ) using methods well known in the art ( see , e . g ., baker , et al ., “ controlled release of biological active agents ,” john wiley and sons , 1986 ). liquid preparations for oral administration can take the form of , for example , solutions , syrups or suspensions , or they can be presented as a dry product for constitution with water or other suitable vehicle before use . such liquid preparations can be prepared by conventional means with pharmaceutically acceptable additives such as suspending agents ( for example , sorbitol syrup , cellulose derivatives or hydrogenated edible fats ); emulsifying agents ( for example , lecithin may serve this function , or acacia ); non - aqueous vehicles ( for example , almond oil , oily esters , ethyl alcohol or fractionated vegetable oils ); and preservatives ( for example , methyl or propyl - p - hydroxybenzoates or sorbic acid ). the preparations can also contain buffer salts , flavoring , coloring and sweetening agents as appropriate . preparations for oral administration can be suitably formulated to give controlled release of the active compound . for buccal or sublingual administration the formulations can take the form of tablets or lozenges formulated in conventional manner . the formulations can be prepared for parenteral administration by injection , for example , by bolus injection or continuous infusion . formulations for injection can be presented in unit dosage form , for example , in ampoules or in multi - dose containers , with an added preservative . the formulations can take such forms as suspensions , solutions or emulsions in oily or aqueous vehicles , and can contain formulatory agents such as suspending , stabilizing and / or dispersing agents . alternatively , the active ingredient can be in powder form for constitution with a suitable vehicle , for example , sterile pyrogen - free water , before use . the formulations can also be prepared in rectal compositions such as suppositories or retention enemas , for example , containing conventional suppository bases such as cocoa butter or other glycerides . the formulations can also be provided as a depot preparation . such long acting formulations may be administered by implantation ( for example subcutaneously or intramuscularly ) or by intramuscular injection . thus , for example , the formulations can be prepared with suitable polymeric or hydrophobic materials ( for example as an emulsion in an acceptable oil ) or ion exchange resins , or as sparingly soluble derivatives , for example , as a sparingly soluble salt . because the action of the new compounds is in the central nervous system , delivery techniques can be designed to permit or to enhance the ability of the formulation to cross the blood - brain barrier . such techniques are known in the art ( for example , see pct wo 89 / 10134 , cloughesy and black , j . neurooncol ., 26 : 125 - 132 , 1995 ; and begley , j . pharm . pharmacol ., 48 : 136 - 146 , 1996 , all of which are incorporated herein in their entirety ). components of a formulation can also be modified ( e . g ., chemically ) using methods known in the art to facilitate their entry into the cns . in some cases , it may be desirable to deliver a compound formulation directly to the nervous system , especially when one or more components of a formulation do not cross the blood - brain barrier . examples of such methods are intraventricular injection ( kordower et al ., exp . neurol ., 124 : 21 - 30 , 1993 ) or installation of an osmotic pump ( e . g ., an alzet ® pump ). another example of such a method is to surgically place an omaya reservoir - shunt with in - line filter into the cisternal space . a compound formulation in an appropriate excipient ( e . g ., phosphate - buffered saline ) is instilled into the shunt by injection on a prescribed basis . in all cases , consideration is given to the appropriate formulation used for specific forms of delivery . for administration by inhalation , a formulation is delivered , for example , as an aerosol spray with the use of a suitable propellant , for example , dichlorodifluoromethane , trichlorofluoromethane , dichlorotetrafluoroethane , carbon dioxide , or other suitable gas . other suitable methods of nasal delivery known in the art can be used , including those that facilitate delivery of a predetermined dosage . the formulations can be presented in a pack or dispenser device , which may contain one or more unit dosage forms containing the active ingredient . the pack may , for example , comprise metal or plastic foil , such as a blister pack . the pack or dispenser device can be accompanied by instructions for administration . the therapeutic formulations of the invention can also contain a carrier or excipient , many of which are known to skilled artisans . excipients that can be used include buffers ( for example , citrate buffer , phosphate buffer , acetate buffer , and bicarbonate buffer ), amino acids , urea , alcohols , ascorbic acid , phospholipids , proteins ( for example , serum albumin ), edta , sodium chloride , liposomes , mannitol , sorbitol , and glycerol . suitable pharmaceutical carriers for intravenous and other parenteral administration include , for example , sterile water , physiological saline , bacteriostatic saline ( i . e ., saline containing about 0 . 9 % mg / ml benzyl alcohol ), phosphate - buffered saline , hank &# 39 ; s solution , or ringer &# 39 ; s lactate . suitable carriers for topical administration include commercially available inert gels , liquids supplemented with albumin , methylcellulose , or a collagen matrix . typical of such formulation are ointments , creams , and gels . preferred carriers for topical administration are those that facilitate penetration of the skin by the new compound . methods for making such formulations are well known and can be found in , for example , remington &# 39 ; s pharmaceutical sciences ( gennaro , ed ., williams & amp ; wilkins , baltimore , md .). the compounds described herein can also be administered as at least one physiologically acceptable salt such as a chloride salt , a bromide salt , or an acetate salt . in one example of the use of the new compounds and methods , a cocaine addict is treated with one of the new drugs , given either orally or systemically . once the half - life of the drug is determined using well - known methods , a dosing regimen ( including dosage and dosing frequency ) is established . in clinical trials of the drugs , tests are used to determine efficacy ( defined , for example , as effectiveness in causing a person treated with the drug to stop using cocaine ). levels of cocaine in the body would also be monitored in the clinical trials . a therapeutically effective amount of the compound is a quantity of compound that , after being administered to an individual who has , for example , an addiction to cocaine , brings about an amelioration of the disease processes and conditions associated with the addiction without causing unacceptable side effects . the practitioner can determine the appropriate dosage for administration to a human or experimental animal patient . the amount of a compound that is administered will depend on a number of factors , including the general health , size , age , and gender of the individual , as well as the route of administration . it will also depend on the degree and severity of the individual &# 39 ; s addiction . typically , however , between about 100 μg and 5 . 0 g , e . g ., 0 . 01 to 10 mg / kg , of the compound can be administered to the individual per day . for example , about 1 to 1000 mg ( e . g ., 1 to 100 mg or 1 to 30 mg ) can be administered orally ( e . g ., in the form of a pill , tablet , syrup , suspension , or capsule ) or nasally ( e . g ., in the form of an inhalant ) each day . the compound can also be administered intravenously ( e . g ., by injection ) into the systemic vascular compartment . still other appropriate modes of administration include systemic administration , intramuscular , intradermal , subcutaneous , intraperitoneal , and topical administration . morphinans labeled , e . g ., with isotopes of fluorine - 18 or iodine - 123 , are useful for studying how brain opioid receptors change when , for example , substance abusers undergo drug withdrawal treatment programs . positron emission tomography ( pet ) and single - photon emission tomography ( spect ) scans can be used for comparing changes in opioid receptor binding from baseline , through drug withdrawal , and through treatment . by comparing the timeline of these changes to changes in patient abuse patterns , researchers can predict time to relapse . successful visualization of receptors with pet or spect requires a ligand that possesses both high affinity and low nonspecific binding . of the commonly used positron - emitting isotopes , fluorine - 18 ( 18 f ) offers considerable advantages , including a relatively long half - life ( 109 minutes ) that permits imaging when receptor - specific binding is at its highest . iodine - 123 ( 123 i ; half - life = 13 hours ) offers similar advantages for spect imaging . in view of their high affinity and low nonspecific binding , compounds 3 and 10 , which include fluorine atoms , and compounds 34 and 35 , which include iodine , are particularly well suited for use in pet and spect imaging , respectively . other compounds in fig1 a and 1b can also be used if properly labeled . the following example , while not limiting the scope of the invention described in the claims , provides additional guidance for the use of the new compounds for imaging . the new morphinans , when properly labeled , e . g ., with isotopes of fluorine - 18 and / or iodine - 123 , are useful for studying how brain opioid receptors change when , for example , substance abusers undergo drug withdrawal treatment programs . in this example , [ 123 - i ] (−)- 3 - hydroxy - n -( e )- iodoallylmorphinan ([ 123 - i ]- mcl - 118 ) was prepared and evaluated by measuring spect regional brain uptake in a baboon brain . (−)- 3 - hydroxy - n -( e )- tributylstannylallylmorphinan was prepared using techniques reported in neumeyer et al ., bioorg . med . chem . lett ., 71 : 2735 ( 2001 ), was converted to the 123 - i labeled compound mcl - 118 by the procedure of baldwin et al ., nucl . med . biol ., 20 : 597 ( 1993 ), a procedure used for the conversion of methyl 3 - beta - 4 - tributylstannylphenyl ) tropane - 2 - beta - carboxylate to [ 123 - i ]- beta - cit . the radiopharmaceutical was formulated in sterile isotonic saline containing about 1 ml l - ascorbic acid and 5 % ethanol , ph was 6 . 5 . 1 . 09 mci of the radiopharmaceutical was administrated through an intravenous line . data were acquired with a brain - dedicated spect camera performed with the as - spect device ( digital scintigraphics , cambridge , mass .). the brain activity ( kbg / ml ) and distribution over four hours is shown in the graph in fig5 . in the graph , fc stands for the frontal cortex , pc — piriform cortex , bg — basal ganglia , cb — cerebellum , ha — hypothalamus , oc — occipital cortex , tic — temporal cortex , and cc — cengulate cortex , which are all areas of the brain . the data show high uptake within 15 - 30 minutes in those areas of the brain ( oc , thalamus , brain stem , cc , and pc ) containing the highest concentration of kappa and mu receptors . in addition , the radiopharmaceutical is almost completely washed out in 4 hours from all areas of the brain . it is to be understood that while the invention has been described in conjunction with the detailed description thereof , the foregoing description is intended to illustrate and not limit the scope of the invention , which is defined by the scope of the appended claims . other aspects , advantages , and modifications are within the scope of the following claims .
the invention is based in part on the discovery that nonselective κ agonists that possess μ receptor - mediated effects in addition to their κ agonist effects can decrease cocaine self - administration more effectively and with fewer undesirable side effects than can highly selective κ agonists . the invention includes a number of new compounds having both nonselective κ opioid receptor agonist activity and additional activity at μ opioid receptors . these compounds are useful for the treatment of cocaine abuse , and can also be radiolabeled for use as imaging agents , e . g ., the n - fluoroalkyl and iodoalkyl derivatives can be used , respectively , for positron emission tomography and single photon computed tomography brain imaging .