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J . M e d . C h e m . 1988 ,31, 1625-1628 1625metha nol was ad ded dropwise a solution of 3.1 g (10 mmol) of4c an d 2.20 g (58 mmol) of NaB H4 in 20 mL of methanol. Halfwaythroug h thi s addition, a second portion of 2.6 mL of 6 N HzSO4was added t o the reaction. Th e resulting mixture was stirred atroom temperatu re for about 4 h. Analysis of th e reaction mix tureby TLC indicated the presence of mostly starting material. Th ep H of the reaction was adjusted to 4 (methyl orange) with 15%HC1. Additional formaldehy de was add ed (3.0 mL, 40 mm ol),followed by 2.51 g (40 mmol) of NaCNBH3 . After 30 min, excessHCl was added, and the mixture was concentrated in vacuo. Th eresidue was partitione d between CH2 Cl2 nd 5% ,OH. Th eorganic layer was dried over Mg S0 4and evaporated. Th e residuewas purified by MPLC (70% heptane, 29% EtOAc, 1% ,OH)to yield 0.50 g (15% ) of 4 f m p 89-93 C; NM R (CDC13) 61.98-2.08 (2 H, m ), 2.58-2.69 (6 H, m ), 2.95 (6 H, s), 3.20-3.26(4 H, m) , 4.06 (2 H , t, J = 6.4 Hz ), 6.30-6.41 (3 H , m), 6.84-6.98(3 H, m), 7.11-7.33 (3 H, m); MS, m/ z 339 (M, 71), 175 (100). Anal.(CziHzsN30) C, H, .P h a r m a c o l o g i c a l M e t h o d s . [ 3 H ] H a l o p e r i d o l R e c e p t o rBi nd in g Assa y. Th e af f ini t ies of compounds for brain DAreceptors were determine d by stan dard receptor b inding assay , 'according t o m ethod s described previously.*E f f e c t s on th e Firing Rate of S u b s t a n t i a N i g r a D ANeurons.14 Th e action potential of zona compacta DA cells wasrecorded in chloral anesthetized rats by using standard extra-cellular recording techniques. DA cells were identified bywaveform and fir ing pattern and recording sites were verif iedhistologically. Drugs were adm inistere d intraperito neally via anindwelling cathe ter. Base-line fir ing rate was calculated by av-eraging the rate over the 2 min prior to drug injection. D rug effectswere determined by averaging the response during the 1-minperiod of maximal inh ibition . D rug-in duce d inhib ition of firingwas reversed with th e DA antagonist haloperidol to confirm a DAagonist mechanism.I n h i b i t i o n s o f s p o n t a n e o u s l o c o m o t o r a c t iv i t y a n d m o t o rcoordin ation1 6 were carried o ut according to methods describedpreviously.(22) (a) Wise, L. D.; Pattiso n, I. C.; Butler, D. E.; DeWald, H. A, ;Lewis, E. P.; Lobbestael, S. J.; Tecle, H.; Coughenour, L. L.;

Downs, D. A.; Poschel, B. P. H. J.Med. Chem. 1985 ,28, 1811.(b) Wise, L. D.; Butler, D. E. ; DeW ald, H. A.; Lustgarten , D.;Coughenour, L. L.; Downs, D. A,; Heffner, T. G.; Pugsley, T.A. J.Med. Chem. 1986,29, 1628.

I nh ib i t ion of GBL- S t imula ted DA Synthesis.15 Compoundswere administered to rats 1h before sacrifice, and y-butyrolactone(GBL, 750 mg/ kg ip) and N SD 1015 (100 mg/kg ip) were ad-mini stered 30 and 25 min , respectively, before sacrifice. Bra inlevels of dihydroxyphenylalanine (DOPA ) were analyzed by H PL Cwith e lect rochemical de te ~ t i on . ~E f f e c t s o n S p o n t a n e o u s Lo c o m ot io n i n R e s e r p i n i z e d R a tvs N o r m a l Rat.18 Drugs were administered subcutaneously tonormal rats treated with 5 mg/k g of reserpine 24 h prior to testing.Locomotor activity was measured for 30 min beginning imm e-diately after drug administration as described pre~iously.~~E f f e c t s on Spon taneou s Locomot ion in 6- OHDA Les ionedRats.19 Drugs were adm inistere d subcutaneously to rats treate dat least one month previously with central injections of 6-hydroxydopamine (6-OHDA, 200 pg icv) and systemic injectionsof pargyline (50mg/kg ip) and desmethylimipramine (25 mg/kgip) as descr ibed previou~ly. ~This t reatm ent produced largeselective deple tion of brain DA (approx imately 90% ) as describedpreviouslyz4 and a s determ ined by b rain DA d etermin ations inrepresentative animals. Locomotor activity was measured for 30min beginning immediately after drug administration as describedp r e v i o ~ s l y . ~ ~ ~ ~S i d m a n a v o i d a nc e p r o c e d u r ez 0a n d e x t r a p y r a m i d a l s i d ee f f e c t testz1 n mature squirrel monkeys were performed asdescribed previously.22Acknowledgment. We wish t o t ha nk C. L. C h r i s t o f -fersen, L. L. C o u g h e n o u r , J. N. W i l e y , and A. E. W i l l i a m sf o r b i o l o g i ca l data.R e g i s t r y N o . 2, 73966-53-7; 3, 85976-54-1; 4a, 114597-68-1;4a.2HC1, 114597-69-2; 4b, 114597-70-5; 4c, 85868-45-7; 4d,114597-71-6; 4e, 114614-34-5; 4f, 114597-72-7; 5, 621-42-1; 6,78702-97-3; 7a, 114597-73-8;7b, 114597-74-9;7c, 78702-84-8; 7d,

l -b romo-3-ch lo ropropane , 109-70-6; 1,2,3,6- tetrahydro-4-phenylpyridine dihydrochloride, 114597-76-1; 1-(2-pyridinyl)-piperazine, 34803-66-2; 1-phenylpiperazine, 92-54-6; N-propy l-phenethylam ine, 27906-91-8.

114597-75-0; 8c, 10599-17-4; 8~*2 HC1,935 07-98-3;, 78702-83-7;

(23) Myers, S.; Pugsley, T. A. Brain Res. 1986,375, 193.(24) Heffner, T. G.; Seiden, L. S. J.Pharmacol. Erp. Ther. 1979,208, 134.

Synthesis, Pharmacological Action, and Receptor Binding Affinity of theEnantiomeric I-(1-Phenyl-3-methylcyclohexy1)piperidinesAndrew Thurkauf, Paul H i l l er y , M a r i e n a V. Mattson, Arthur E. J a c o b s o n , and Ken ner C. Rice*Sec t i on on Drug Des i gn and S yn t h es i s , L abora tory o f Neurosc i ence , Nat i ona l In s t i t u t e o f Di abe t es , D i ges t ive and K i dn eyDi seases, Nat i ona l I ns t i t u t e s o f H e a l t h , B e t h e s d a , M a r y l a n d 20892. Received August 26 , 1987

The cis and tra ns enantiomers of the l-(l-phenyl-3-methylcyclohexyl)piperidinesere prepared from either 3(R)-or 3(S)-methylcyclohexanone hroug h th e Bruylen ts reaction or a modified azide route, respectively. Separatio nof the intermediate amines 5 an d 6 was achieved throug h chromatograph y or selective crystallization of a fum aratesalt. Th e cis isomer 2b had abo ut one-third of th e affinity of phencyclidine for the P C P receptor. Th e other isomerswere less potent. Th ere was a 40-fold difference between th e binding affinity of the cis enantiomers 2a and 2b anda fourfold difference between t he affinities of th e tran s enantiom ers la and I b. None of the compounds antagonizedthe stereotypy induced by phencyclidine in the rotorod assay in mice, after intraperitoneal introduction.In 1981,V i n c e n t e t a1.l e x a m i n e d the s t r uc tur e - ac t iv i tyr e l a t i o n s h i p s of v a r i o u s d i a s t e r e o m e r i c p a i r s o f 1-(1-phenyl-2-methylcyclohexyl)piperidinesnd the 3 - m e t h y land 4 - m e t h y l i s o m e r s . Those c o m p o u n d s h a v i n g them e t h y l and p h e n y l g r o u p on t h e s a m e s i de or face of the(1) Vincent, J. P.; Vignon, J.; Kartolovski, B.; Lazdunski, M. PC P(Phe ncyc lidine) : Historical and Cu rrent Perspe ctives; Dom-ino, E. F., Ed.; NPP Books: 1981;p 83.

c y c l o h e x y l r i n g w e r e r e f e r r e d to as c i s c o m p o u n d s ; t h o s ew i t h m e t h y l and p h e n y l on o p p o s i t e s i d e s w e r e c a l l e dt r am1 For t h e p u r p o s e o f s i m p l ic i t y w e r e t a i n thesed e f i n i ti o n s w h e n r e f e r r in g t o t h e d i a s t e r e o m e r s. P o t e n -t i al l y i m p o r t a n t d i f fe r e n ce s i n the r e c e p t o r b i n d i n g andbeha vioral ch aracter is t ics of some of thes e pairs of faciali s o m e r s were n o t e d . F o r i n s t a n c e , w h i l e the af f in i t i e s o fthe 3 - m e t h y l c y c l o h e x y l c i s and 3 - m e t h y l c y c l o h e x y l t r ans d ias te r eomer s f or the phencyc l id ine ( PCP ) r ecep t, o r

Thi s ar t ic le no t subject to US. opyright. Publish ed 1988 by the American Chemical Society

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1626 Jour na l of Medicinal Chemistry, 1988, Vol. 31, No. 8C h a r t I

Thur kauf e t a l .S c h e m e I

H h

1: ( T R R N S ) R, P h , R, = 1 - P I P E R I D Y L2 : ( C I S ) R, = 1 - P I P E R I D Y L , R, = P h

2 a 2 b

T a b l e I. Binding Affinity of the Enantiomeric1-(1-Phenyl-3-methylcyclohexyl)piperidinesa

compound Ki, pM compound K ; ,LLMtra ns -la 0.82 (f0.03) (+)-PCM Pb 0.06 (h0.007)cis-Za 6.8 (k0.54) PCP 0.06 (f0.011)cis-2b 0.17 (f0.03)Displacement of [3H ]TC P rom tissue homogenate preparationof whole rat brain minu s cerebellum. Th e Ki values were deter-mined from displacement data run in triplicate and are the mean(fstandard deviation) of the results from at least three separateexper iments . 1-(l-Phenylcyclohexyl)-3-methylpiperidine,

t rans- lb 3.3 (k0.96) (-)-PCMPb 2.15 (f0.61)

Phencyclidine [1-(1-phenylcyclohexyl)piperidine].were found to be similar (ICw = 0.6KM) n a displacementassay, they showed a large difference in behavioral activity.Th e tra ns diastereomer was behaviorally active in th e ro-torod assay; the cis diastereomer was much less active.These findings suggested to us the possibility th at one ofthe enantiomers in these diastereomers might have P C Pantagon ist activity an d led us t o examine more closely the1-( -phenyl-3-methylcyclohexyl)piperidinesomers throughthe p repara tion and isolation of the enantiomeric sets oftrans (la,b)and cis (2a,b) somers (Chart I). We havedeterm ined their affinity for the PCP receptor and havemade a preliminary assessment of their pharmacologicalactivity using a rotorod assay.Phencyclidine is a poten t psychotomimetic agen t th atrivals heroin and cocaine in level of abuse. It is nowgenerally accepted, on th e basis of several lines of evidence,th at a t least some of the pharmacological effects of PC Pare mediated through i ts interact ion with the PCP re-ceptor; however a specific receptor antag onist has yet tobe identified. One of the generally accepted requirementsfor a receptor to be defined as such is that such a siteshould show stereospecificity of binding to the opticalisomers of the ligand for which it is defined. Unfo rtu-nately, the achiral nature of PC P itself precludes i t frombeing used for this purpose. While a num ber of agents tha thave been shown to be competitive with P C P at this sitedo show enan tiomeric selectivity (dexo xadrol,2 N-allyl-n o r m e t a ~ o c i n e , ~K-8014), they are s tructura lly very

(2 ) Hampton, R. Y.; Medzihradsky, F.; Woods, J. H.; Dahlstrom,P. J. Life Sci. 1982, 30, 2147.(3) Zukin, S. R.; ukin, R. S.Proc. Natl. Acad. Sci. U.S.A. 1979,76, 5372.

3 2Scheme I1

4 : 3 R O R 3 5 5 a : R L = C H l , R , = H 6 a : R , = C H 3 , R , =HR OR 3 5( 1 S . 3 R ) ( 1 R . 3 R )5 b : R , = H , R 2 = C H 3 6 b : R 1 = i , R 2 = C H J( 1 R , 3 5 ) ( 1 S , 3 5 )

H n h

H n

l b : 1 R , 3 Sb : 1 R , 3 5 8 b : 1 R , 3 S

different from PCP . However, a pair of enantiomers from1 (l-phenylcyclohexyl)-3-methylpiperidinePCM P), whichare structurally qu ite similar to P CP , were shown to havea distinct difference in binding ( Table I) and behaviorala ~ t i o n . ~ e thought tha t the enantiomers of the c is andtrans diastereomers of the 1-( -phenyl-3-methylcyclo-hexyl)piperidines, which also retain a close stru ctu ral re-semblance to PCP , might prove to have affinity and ste-reoselectivity for the PCP receptor comparable to theaforementioned PCM P5 compounds.Chemistry

Th e compounds were prepared from ei ther 3(R)- or3(S)-methylcyclohexanone. As has been shown,6 3(R )-methylcyclohexan one is comm ercially available as opticallypure material . The optically pure unnatu ral 3(S )-methylcyclohexanone was obtained by using a practicalprocedure developed in our laboratory.6 Th e cis enan-tiomers 2a and 2b were prepared from th e amino nitrilederivatives 3 via the Br uylan ts reaction as described byMaddox7 (Scheme I). Th e Bruy lants reaction is knownto give only cis products. Th us , with pure 3(R)-methyl-cyclohexanone6 as th e starting material, only the R,Rcompound 2a could be obtained. Similarly, the S,S com-pound 2b was the only compound obtained from theBruylants reaction when pure 3(S)-methylcyclohexanone6was used as the starting material. Th e trans derivativesla and l b were prepared via a modification of the azideroute of Geneste.8 Certain modifications were applied to

Wone. E. H. F.: KemD. J. A.: Priestlev, T.: Knight, A. R.;Woodruff, G. N.; Iversen, L. L. Proc. Nail. Acad. Sci. U.S.A.1986, 83, 7104.(a) Quirion, R.; Rice, K. C.; Skolnick, P.; Pau l, S.;Per t , C. B.Eur. J . Pharmacol. 1981, 74,107. (b) Marwaha, J.; Palmer, M.;Hoffer, B.; Freedman, R.; Rice, K. C.; Paul, S.; Skolnick, P.Naunyn-Schm iedebergs Arch. Pharmacol. 1981, 315, 203.Thurkau f, A.; Hillery, P.; Jacobson, A. E.; Rice, K. C. J . Org.Chem. 1987,52, 5466.Maddox, V. H.; Godefroi, E. F.; Parcell, R. F. J . Med. Chem.1965, 8, 230.Geneste, P.; Hermann, P.; Kamenka, J. M .; Pons, A. Bull . SOC.Chim. Fr. 1975, 1619.

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I - ( I -Phenyl-3-methylcyclohexyl)piperidinesthis pathw ay, which, although requiring two add itionalsynthetic steps, led to a more satisfactory overall yield.Scheme I1 shows the overall preparation. Phe nyllit hiumwas condensed with t he ap propriate cyclohexanone to givethe tertiary alcohol 4. Trea tmen t with sodium azide andtrifluoroacetic acid followed by reduction of the resultingazide gave a 7:3 mixtu re of tra ns (5) to cis (6) amines.Since the reaction pathway gave both tra ns an d cis com-pounds, th e a mino compounds 5a and 6a were obtainedwhen 3(R)-methylcyclohexanone as the starting material,and 5b and 6b were obtained from 3(S)-methylcyclo-hexanone. Compounds 5a and 6a are diastereomers, asare 5b and 6b, and thus are easily purif ied a nd differen-t ia ted by GC and TLC. The amines 5a and 6a could beseparated from their diastereomers 5b an d 6b,respectively,by selective crystallization of th e tran s ami ne as its fu-mara te salt. Th e preparation of the piperidine ring, usuallyaccomplished by the use of 1,5-dibromopentane, was foundto proceed in considerably better yield (72% vs 41 5%) bythe three-step process of N-acylation with 5-chloro-propionyl chloride, followed by cyclization to the valero-l ac tam and r educ tion to g ive t r an s - l - ( l - pheny l -3 -methylcyclohexy1)piperidine la or lb . Th e cis amines6a an d 6b were not utilized since they lead to the ciscompounds 2a a nd 2b, which had been obtained via theBruylants reaction.Results and Discussion

The receptor binding affinity of the enantiomers of thetrans- and cis-l-(l-phenyl-3-methylcyclohexyl)piperidine(la, lb and 2a, 2b) assessed on the basis of competitiveinhibition of tritiated l-(2-thienylcyclohexyl)piperidine( t3H]TC P) binding to rat b rain tissues is shown in TableI. All of these compou nds were shown to have less affinityfor the P C P receptor than phencyclidine itself. When th ebinding affinities of the en antiom ers la + lb and 2a+ 2bar e averaged, th e racemic values thu s obtained are fairlysimilar for the tran s and cis pairs, in agreement withthe da ta of Vincent e t a1.l However, inspection of thebinding da ta for the individual enantiom ers reveals dis-tinctly d ifferen t binding affinities for the isomers in thecis and trans pairs. This is most pronounced for thecis compo unds (2a, 2b),where the 3(S)-methylcyclohexy1enantiomer (2b)showed a 40-fold greater ability to displace[3H]TCP tha n did the 3(R)-methylcyclohexy1 enantiomer(2a). Within th e t rans pair (la, lb) a smaller affinitydifference (4 times) is found. Th e cis compounds 2a and2b were somewhat less poten t, although they were a littlemore enantiomerically selective, in binding to the PCPreceptor tha n the PC M P isomers (Table I). The methylsubstitu ent on the cyclohexane r ing of P C P (in 2b) less-ened the affinity of the molecule to the PCP receptor,unlike a methyl sub stitu ent on the piperidine ring of thePC P m olecule ( in the (+)-PC MP isomer), which had li tt leor no effect on receptor binding, as compared with PCPitself (Table I). The enantiomerically selective binding ofthe cis-l-(l-phenyl-3-methylcyclohexyl)piperidines2aand2b) and th e P CM P isomers lends credence to the presenceof a distinct b inding site for phencyclidine within a chiralmatrix.Vincent e t a1 . l no ted that the c is - l - ( l -phenyl-3-methylcyclohexy1)piperidinemixture h ad affinity for thePC P receptor an d th at the cis mixture had little behavioraleffect as measured by the rotorod assay. Th is lead us tospec ulate on the possibility of antagonistic qualities re-siding within one of these enantiomers. Prelim inarytesting of compounds 2a and 2b agains t PCP with therotorod a ssay, in mice (N IH colony, 20-25 g) injected in-traperitoneally in doses representing up to 10 t imes the

Journal of Medicinal Chemistry, 988,Vol. 31 , No. 8 1627P C P dose, indicated only potentiation of P C P stereotypyfor bot h enantiomers. No antagonism of the stereotypyinduced by P C P was noted.Experimental Section

Melting points were obtained on a Thomas-Hoover meltingpoint apparatus a nd are uncorrected. IR spectra were obtainedon a Beckm an 4230 spectrometer, CI mass spec tra were obtainedon a Finnigan 1015D mass spectrometer with NH 3 as the reagentgas, and H NMR spectra were obtained on a Varian XL-300spectrometer. GC was performed on a Hewlett-Pa ckard 5880Ainst rum ent throu gh a 12-m OV-1 capillary column, with a flameionization detector. Optical rotations were obtainedr with aPerkin -Elme r 241MC polarimeter. All reported optical rotation swere obtain ed on free bases dried under high vacuum. Th e freebases were obtained from their pure amine salt, after th e salt hadbeen crystallized t o a constan t melting point.1-(1(R)-Phenyl-3(R)-methylcyclohexy1)piperidine 2a).Compound 2a was prepared in 54% overall yield from 3(R)-methylcyclohexanone according to the me thod used by Kalir et

al? for th e preparation of the racemic material. Th e final productswere purified by recrystallization of th e hydrochloride salt s fromethyl acetate/hexa ne: m p 114-116 C (HC1 salt) ; TL C R, 0.74(2.5% MeO H/CHC 13/1% ,OH); (free base) [aIz5~35.1 ( c3.75, CHCl,); IR (nea t) 2860,1 440,11 50,106 5,945 cm-; H N MR(CDCl,) 6 7.3 (m, 5 H), 2.60 (dd ,J = 14.4, 14.4 Hz, 2 H ), 2.22 (m,3 H), 1.95 (m, 1 H ), 1.85 (ddd, J = 13.2, 3.5, 3.5 Hz! 1 H), 1.75(d , J = 14.1Hz, 1 H ), 1.0-1.6 (m , 11H), 0.91 (d, J = 6.5 Hz, 3H ) ; C I MS, m/z 258 (M + H). Anal. (Cl,Hz7N-HC 1) C, H , N.1-( 1(S)-PhenyL3(S)-rnethylcyclohexyl)piperidine 2b).Compound 2b was prepared in 48% overall yield from 3(S)-methylcyclohexano ne by using the procedure previously describedfor compound 2a: mp 114-115 C (HC1 salt); spectrally identicalwith 2a except for optical rotation; (free base) +34.8 (c1.59, CHC l,). Anal. (C18Hz,N.HC1) C, H , N.l - P h e n y l - J ( R ) - m e t h y l c y c l o h e x y l a m i n e (5a, a). Phenyl-lithium solution (1.1 equiv) was added dropwise at 0 C to asolutio n of 3 g (26.7 mmol) of 3(R)-methylcyclohexanone n 50mL of dry ether. After 10 min th e reaction was carefully pouredinto a separatory funnel containing 150mL of 0.1 N HC1. Theorganic layer was removed, dried with NaSO,, a nd con centrate dto give 3.7 g (73%) of a mixtu re of isomeric 1-phenyl -3-meth yl-cyclohexanols (4).Th is mix ture (19.5 mmol) was dissolved in 80mL of chloroform,and an argon atmos phere was applied to the resulting solution.Pow dered sodiu m azide (2.53 g, 39 mmol) was add ed, followedby 4.45 g (3.0 mL, 39 mmol) of trifluoroacetic acid. Th e violetmixture was stirred for 9 h, during which time th e suspended solidmater ial became a paste. Th e reaction was poured into a sep-aratory funnel with 50 mL of water an d 50 mL of saturated sodiumbicarbonate solution. Th e organic layer was removed, dried(NaSO,), and concentrated.Th e conce ntrated m aterial (4.0 g) was dissolved in 90 m L ofdry ether , and 1.5g of powdered lithium aluminum hydride wasadded in portions at 0 C. Th e resulting mixture was then refluxedfor 30 min. After cooling, 2 mL of ethyl acetate was added tothe solution and the mixture was carefully poured in to a separatoryfunnel containing 100mL of 1.0N HC1. Th e mixture was carefullyshaken. Th e aqueous layer was returned to th e funnel, aqueousammonia was added until th e mixture was basic to p H paper, an dth e resulting solution was extracted with ether (3 X 50 mL). Thecombined extracts were dried (NaSOJ and co ncentrated to give770 mg (21% ) of isomeric amines. Gas chromatograp hic analysis(at 130 C, retention t imes: 5a,3.05 min, and 6a, 3.62 min)indicated a 7 to 3 ratio of 5 to 6. Th e separation of the diaste-reomers 5a and 6a (or 5b an d 6b ) could be successfully achievedeither by column chromatograph y or by separation of 5a ro mthe m ixture by selective crystallization as its fuma rate salt fromethy l acetate (see proce dure below). Assignment of th e relativestereochemistry of these compoun ds was made after conversionof the pr imary amines to the co rresponding piperidines la an d2a an d subsequent compar ison of their lH N MR spectra with

(9 ) Kalir, A. ; Sadeh, S.; Karoly, H.; Shirin, E.; Balderman, D.;Edery, H.; Porath, G. Isr. J . Chem. 1975, 13 , 125.

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1628 J o u r n a l of Medi c i na l Chemi s t ry , 1988, Vol. 31, No. 8those of the known trans and cis racemates 1 and 2.8 Theirabsolute stereochemistry and enantiomeric purity t hen followedfrom the previously established (> 98% ) enantiomeric purity ofthe 3(R)- and 3(S)-methylcyclohexanone.6 Since the reac tionconditions employed were highly unlikely to affect the isolatedchiral center of the 3-methylcyclohexanones, greater th an 98%purity followed for the pro ducts. Diastereomeric purification of5a and 6 a was easily followed by TL C and GC. It was experi-menta l ly found tha t a 0.1% diastereomeric impurity was dis-cernable by GC (see the exp erimental cond itions below). Com-pounds Sa a nd 6a (a nd 5b a nd 6b ) ha d l e ss tha n 0.1% diaste-reomeric impurity.S e p a r a t i o n of the D i a s t e r eo m e r i c A m i n e s 1(S ) - P h e n y l -3 ( R ) -m e t h y l c y c l o h e x y l a m i n e ( 5 a ) a n d 1 R - P h e n y l - 3 ( R ) -me thy lcyc lohe xyl am ine (6a) . A mixture of amines 5a and 6a( 7 :3 atio, 1.0 g) was dissolved in 20 mL of EtO Ac. A solutionof 430 mg of fumaric acid (0.7 equiv) in 6 mL of ho t methan olwas added to p roduce a crystalline precipitate. After cooling, th eprecipitate (700 mg) was collected and recrystallized from 2-propanol to g ive 590 mg of 5a-C4H 40, 59%): m p 220-221 "C;(free base) [.]25D -20.1" (c 0.77, metha nol). Anal. (CI3Hl,N-C4H404) C, H, N. After conversion t o the free base with con-centrated ",OH, the moth er liquor was separated by columnchromatography (silical gel, 94% CHC13/5% M eO H /l% ",OH)to give 281 mg of 6a a nd a n add itional 178 mg of 5a.In order to confirm that the GC assay method used for de-termination of diastereomeric purity during the separation of 5afrom 6a (or 5b from 6b) was accurate to 0.1%, the following testwas performed. A stand ard solution of 5a (0.01M) was prepared,a n d 0.05 mL of this solution was added to 10 m L of Me OHcontaining 94.5 mg of 6a. Th is 0.1% "impurity" of 5a in the 6awas easily discerned by GC. Th e diastereomeric purity of 5a and6a (and 5b a nd 6b) assures the d ias tereomeric purity of l a a n dl b since the reaction conditions employed could not have alteredthe stereochemistry. T h eoverall yield of 5b a nd 6b was 68% , an d the same diastereomericra t io of 5b to 6b was obta ined as 5a to 6a . For 5b C4H 404 :m p171-173 "C; (free base) [a]25D0.9" (c 0.77, methanol).1 R - P h e n y l - 3 ( R ) - m e t h y l c y c l o h e x y l a m i n e (6 a ). F o r6a .C4H404: m p 203-204 "c; free base) [.I2'D -7" (c 0.024,methanol) .1( S -Phe ny l -3 ( S - m e thy lc yc lo he xy la m ine (6b) . Fo r 6b.C4H404 mp 201 "c ; (free base) [.IDz5 +To (c 0.024, methano l).N- 1(S - P h e n y l - J ( R - m e thylcyclohexyl)-5-chlorovaler-am id e (7a). Th e fuma rate salt of 5a (0.49 g, 1.61 mmol) wasdissolved in a two-phase m ixture of 5 mL of CHC1, an d 5 mL ofsaturated sod ium carbonate solution. T he mixture was rapidlystirre d as 249 mg (1.61 mmol) of 5-chlorovaleryl chloride in 1.0m L of CHCl, was add ed via syringe. After 20 min th e CHC1,phase was removed by p ipette, th e aqueous layer was washed withanother 2 m L of CHCl,, a nd th e combined organics were driedby passage through a short column of MgSO,. Con centra tion ofth e filtrate gave 455 mg (92 % ) of th e chloroamide 7a as an oil:T L C R, 0.47 (30% EtOAc/hexane); IR (neat) 3300,30 60, 2950,2860,1640,1540,1485 cm-'; 'H NMR (CDC1,) 6 7.52 (d, J = 7. 5Hz , 2 H) , 7.35 (d d J = 7.5 Hz, 2 H), 7.24 (m , 1H) , 5.44 (br, 1 H ,NH ), 3 .48 (t ,J = 6.1 Hz, 2 H) , 2 .68 ( t , J = 14 Hz, 2 H ), 2.05 (m,4 H) , 1.0-1.8 (m , 10 H), 0.91 (d, J = 6.7 Hz, 3 H) ; CI MS, m / z308, 310.N - (1(R)-Phenyl-3(S)-methylcyclohexyl)-5-chlorovaler-am ide (7b). The amide was obtained as an oil. T he spectral dataand MS were identical with those obtained with 7a.N - 1 S -Phenyl-3(R ) -me thy lc yc lohe xy l ) 6 -va le ro la c ta m(Sa). I n a dry 25-mL side-arm flask containing an argon atmo-sphere, a quantity of sodium hydride (ca. 150mg, 80% in oil)waswashed twice with isooctane a nd th en covered with 4 mL of dr yether. To this solution was added 450 mg of th e chloroamide 7a(1.4 mmol) in 4 mL of e ther , and t he resulting solution wasrefluxed until the starting material was undetectable by thin-layerchromatograph y (3 h). Th e solution was then cooled to roomtemperature, and the excess hydride destroyed by the additionof a few drops of water. T he reaction mix ture was filtered througha Celite pad , and the pad was subsequently washed with 10 m Lof ether. T he filtrate was concen trated to give 348 mg of the cyclic

1 R - P h e n y l - 3 (S ) - m e t h y l c y c l o h e x y l a m i n e ( 5 b ) .

T h u r k a u f e t al .amide 8 (92% ). While the material was of sufficient purity toproceed with th e reaction sequence, a portion of the mixture waspurified by chromatography (30% EtOA c/hexane) t o give pure8 as an oik TL C R, 0.36 (30% EtO Ac/h exane ); (free base) [.Iz5D-15.1" ( c 3.08, MeOH ); IR 2945, 2870,1643, 1455 cm-l; 'H NM RHI, 7.19 (m, 1H) , 3.28 (t , = 5.7 Hz, 2 H) , 2.9 (m, 3 H) , 2.24 (t ,J = 6.6 Hz, 2 H) , 1.0-2.05 (m, 10 H) , 0.89 (d , J = 6.3 Hz, 3 H ) ;C I MS, m/z 272. Anal. (Cl8HZ6NO)C, H.N- ( (R)-Phenyl-3(S)-methylcyclohexyl)-6-valerolactam(8b). Spec tral data were identical with those of Sa: CY]^^^ f15.4'(c 3.08, MeOH ).1-(l(S)-Pheny1-3(R)-methylcyclohexyl)piperidine l a ) .Th e cyclic amid e 8 (300 mg, 1.1mm ol) was dissolved in 1 8 mLof dry TH F. Powdered lithium aluminum hydride (540 mg) wasadded in portions, and the m ixture was refluxed for 1h, cooledto 10 "C, and qu enched by the successive addition of 0.54 mLof water, 0.54 mL of 1.0 N N aOH solution, and 1.1mL of water.An additio nal 20 mL of ether was add ed, and the solution wasstirred for 20 min, filtered through MgSO,, an d concentrated. T hecrude material was taken up in 10 mL of EtOAc, and 128 mg offumaric acid in 3 mL of hot methano l was added. Th e mixturewas then heated to d issolution and allowed to cool, giving 344mg of fumarate salt of l a (84%): mp 197-198 "C dec; TL C R ,0.10 (2.5% MeO H/CHC 13/1% ",OH). Free base: [ 0 I z 5D -32.3"(c 0.027, CHCI,); lH N MR (CDC1,) 6 7.3 (m, 5 H ), 2.62 (m, 2 H ),2 .28 (m, 3 H ), 1 .65 (ddd , J = 12.0, 3.0, 3.0 H z, 1 H) , 1.0-1.6 (m,13 H), 0 .89 (d , J = 7.1 Hz, 3 H); CI M S, m/z 258. Anal. (el8-

l-(1(R)-Phenyl-3(S)-methylcyclohexyl)piperidine l b ) .Fumara te sa l t , prepared as with l a , m p 196 "C dec. Compoundl b was spec tra l ly ident ica l wi th l a except for optical rotation,[@]"D +33.5" (c 0.021, CHC1,) (free base). A nal. (Cl8H Z7N C4H 4O4 )C , H , N .Bin din g S tudi es . Th e displacement assays were performedas previously desc ribed by Jac obso n et al.,1 with a t issue hom-ogenate preparation of fresh whole rat brain m inus cerebellum.Incubat ion was carr ied out a t 5 "C with [3H]TCP as the radio-ligand. Rapid filtra tion was done throu gh filters presoaked with0.03% polylysine. T he inhibition constant (K , ) or determinationof the compou nd for the P CP receptor was calculated by usingth e Cheng-Prusoff equat ion,ll employing our determ ined KdforTCP (16.5 nM) from Scatchard analysis . Experiments wereperformed in triplicate, and 10 pM TCP was used for determi-nation of nonspecific binding. T he Kivalues listed in Table I werethe m ean values (A tandard deviation) from at least three sep-ara te experiments .

Acknowledgment. P.H., f r o m t h e F o o d and D r u gA d m i n i s t r a t i o n , R o c k v i l le , MD 2 0 8 57 , w a s s u p p o r t e d asan NIH Guest W o r k e r . A.T. wa s s u p p o r t e d b y t he Na-t i o n a l I n s t i tu t e o n D r u g A b u s e t h r o u g h N a t i o n a l R e s e a r c hSe rv ic e Award No. 5 F 3 2 D A 0 5 2 8 7 - 0 2 . A.T. a l s o g ra t e fu l lya c k n o w le d g e s p a r t i a l s u p p o r t f r o m K e y P h a r m a c e u t i c al sInc., G. D. Searle and Co., and t h e C o m m i t t ee on P r o b l e m sof D r u g D e p e n d e n c e . W e t h a n k N. F. W h i t t a k e r , LAC,NIDDK, NIH, f o r the m a s s s p e c t r a l data.R e g i s t r y No. la , 114760-75-7; 1a C4 H4 04 , 14817-20-8; lb ,114760-76-8; lb C 4H 40 4, 14817-21-9; 2a, 114760-65-5; 2a.HC1,114760-67-7; 1R,3R)-4, 114760-68-8;5a , 114760-69-9;5a C 4H4O4,114817-16-2; 5b, 114760-71-3; 5b-C4H404,114817-17-3; 6a,114817-19-5; 7a, 114693-38-8; 7b, 114760-73-5;8a, 114693-39-9;8b, 114760-74-6; PCP, 77-10-1; (3R)-methylcyclohexanone,13368-65-5; phenyllithium, 591-51-5; 5-chlorovaleryl chloride,

(CDC13) 6 7.48 (d, J = 7.5 Hz, 2 H) , 7.30 (dd, J = 7.5, 7.5 Hz , 2

H27NC4H404) C , H , N .

114817-14-0; 2b, 114760-66-6; 2b.HC1, 114817-15-1; (1S,3R)- 4,

114760-70-2; ~C 4H 40 4, 14817-18-4;6b, 114760-72-4; bC4HdO4,

1575-61-7.(10) Jacobson, A. E. ; Harrison, E. A. , Jr.; Mattson, M. V. ; Rafferty,M. F.;Rice, K. C.; Woods, J. H.; inger, G.; Solomon, R. E.;Lessor, R. A. ; Silverton, J. V. J . Pharmacol. Ex p . Ther. 1987,243, 110.(11) Cheng, Y.-C.; Prusoff, W . H. Biochern. Pharmacol. 1973,22,3099.