919
`J . Med. Chem. 1990,33,919-926
`Preparation and Anticonvulsant Activity of a Series of Functionalized a-Aromatic
`and a-Heteroaromatic Amino Acids
`
`Harold Kohn,*it Kailash N. Sawhney,t Philippe LeGall,' Judith D. Conley,t David W. Robertson,$
`and J. David Leandert
`Department of Chemistry, University of Houston, Houston, Texas 77204-5641, and Lilly Research Laboratories, Eli Lilly
`Company, Indianapolis, Indiana 46285. Received July 28, 1989
`
`We recently reported the potent anticonvulsant activity of (R,S)-a-acetamido-N-benzyl-a-phenylacetamide (2b).
`Selectively substituted derivatives of this compound have now been prepared (23 examples) and evaluated in the
`maximal electroshock seizure (MES) and horizontal screen (tox) tests in mice. In several key cases, replacement
`of the a-phenyl substituent in 2b by a relatively small, electron-rich, heteroaromatic moiety led to a substantial
`improvement in the anticonvulsant potency of the drug candidate. The most active compounds were (R,S)-a-
`acetamido-N-benzyl-2-furanacetamide (2g) and (R,S)-a-acetamido-N-benzyl-2-pyrroleacetamide (2i). After ip
`administration, the MES EDa values for 2g (10.3 mg/kg) and 2i (16.1 mg/kg) compared well with phenytoin (9.50
`mg/kg). Evaluation of the two individual enantiomers of 2g demonstrated that the anticonvulsant activity resided
`in the R stereoisomer. The low EDa value (3.3 mg/kg) for (R)-2g contributed to the large protective index (TDw/EDu)
`observed for this drug candidate, which approached that of phenytoin.
`
`Recently we have reported the excellent anticonvulsant
`activities of functionalized amino acid derivatives 1.l+
`0 R2
`R'!NH-/XNHR3
`
`16
`
`H
`1
`
`Table I. Selected Physical and Pharmacological Data in Mice for
`R,S-a- Aromatic and a-Heteroaromatic Substituted Functionalized
`Amino Acid Derivatives 2 O
`
`n2
`I
`CH,CNHCHCNH-CH
`II
`II
`0
`0
`2
`
`
`
`2be
`
`CBH6
`
`4-CeHdOH
`I-CeH,OCHs
`2-OH-5-CH3CeH3
`2-C10H7
`2-furanyl
`
`202-203
`
`232-235
`196-198
`183-185
`210-211
`178-179
`
`5-CH3-2-furanyl
`
`148-150
`
`2-pyrrolyl
`
`174-175
`
`5-CH3-2-pyrrolyl
`
`167-168
`
`>40
`f
`f
`f
`>300
`
`- 40
`
`75.4
`
`>30, C100
`f
`f
`>30, C100
`> 100
`
`H O
`2 a R2 = CH,
`b R 2 - P h
`The pharmacological data suggested that these compounds
`comprised a new and important class of anticonvulsant
`agents? The structure-activity profile for 1 indicated that
`stringent steric and electronic requirements existed for
`optimal anticonvulsant activity. Excellent protection
`against maximal electroshock seizures (MES) in mice was
`observed for functionalized amino acid racemates con-
`taining an N-benzylamide moiety, an acetylated amino
`group, and either a methyl (2a) or a phenyl (2b) substit-
`uent on the a-carbon. The median effective doses (ED,)
`for 2a and 2b in mice (ip) were 76.5 and 20.3 mg/kg, re-
`~pectively.~ These values compared favorably with the
`corresponding EDm value obtained for the proven an-
`tiepileptic phenobarbital (21.8 mg/ kg).' Significantly,
`evaluation of the individual enantiomers of 2a and 2b
`showed that the anticonvulsant activity resided primarily
`In both cases, the R isomer was
`in the R stereoisomer~.~*~?~
`over 10 times more effective in the MES test than the
`corresponding S enantiomer. This difference in activity
`represented the greatest eudismic ratios reported to date
`for MES-selective anticonvulsants.
`The pronounced activity observed for 2b prompted our
`investigation of the anticonvulsant properties of a select
`series of functionalized amino acids in which the a-sub-
`stituent is either an aromatic or a heteroaromatic group.
`In this paper, the synthesis, physical properties, and an-
`ticonvulsant activities of these compounds are described.
`Evidence is presented that placement of a relatively small,
`electron-rich, heteroaromatic moiety at the a-site leads to
`a substantial enhancement in the anticonvulsant activity
`of the drug candidate and that the high eudismic ratio
`observed for 2a and 2b is preserved for the most active
`member of this series of compounds.
`Selection of Compounds
`(R ,S) -a-Acetamido-N-benzyl-a-phenyla~etamide~ (2b)
`
`* Author to whom correspondence should be addressed to at
`the University of Houston.
`'University of Houston.
`1 Lilly Research Laboratories.
`0022-2623/90/1833-0919$02.50/0 0 1990 American Chemical Society
`
`2c
`2d
`2e
`2f
`2g
`2h
`
`2i
`
`2j
`
`2k
`21
`
`179-181
`167-169
`
`198-199
`
`1-CH3-2-pyrrolyl
`2-thienyl
`
`2m
`
`3-thienyl
`
`2n
`benzo[b]furan-2-yl
`indol-3-yl
`20
`benzo[ blthien-2-yl
`2p
`phenytoin8
`
`phenobarbital8
`valproatef
`
`32.1
`(27.5-40.2)
`>300
`>300
`>300
`>300
`10.3
`(9.1-11.6)
`19.2
`(16.4-23.8)
`16.1
`(13.2-19.9)
`36.5
`(30.6-57.1)
`-300
`44.8
`(38.9-51.4)
`87.8
`(69.9-150)
`>loo, C300
`195-196
`>loo, <300
`213-214
`>300
`C300
`226-227 >loo, C300
`>loo, C300
`9.5
`65.5
`(8.1-10.4)
`(52.5-72.1)
`21.8
`69.0
`(15.0-22.5)
`(62.8-72.9)
`272
`426
`'(247-338)
`(369-450)
`a The compounds were administered intraperitoneally. EDw and
`TDw values are in mg/kg. Numbers in parentheses are 95% confidence
`intervals. *Melting pointa ("C) are uncorrected. CMES = maximal
`electroshock seizure test. Tox = neurologic toxicity determined from
`horizontal screen. (Reference 3. /Not determined. 8 Reference 7.
`
`served as the parent compound in this study (Table I). In
`the first series of functionalized amino acid derivatives
`
`(1) Kohn, H.; Conley, J. D. Chem. Br. 1988,24, 231.
`(2) Cortes, S.; Liao, Z.-K.; Watson, D.; Kohn, H. J. Med. Chem.
`1985, 28, 601.
`(3) Conley, J. D.; Kohn, H. J. Med. Chem. 1987, 30, 567.
`(4) Kohn, H.; Conley, J. D.; Leander, J. D. Brain Res. 1988,457,
`371.
`(5) Conley, J. D.; Kohn, H., unpublished results.
`
`IPR2014-01126- Exhibit 1022 p. 1
`
`

`
`920 Journal of Medicinal Chemistry, 1990, Vol. 33, No. 3
`
`Table 11. Selected Physical and Pharmacological Data in Mice
`for Fluoro-Substituted
`(R,S)-a-Acetamido-N-substituted-benzyl-2-furanacetamides
`3
`
`6.
`
`ChCNHCHCNHCH&
`II
`ir
`0
`0
`
`
`3.
`
`toxd
`TDw
`
`- 40
`
`no.
`2g
`
`3a
`3b
`
`3~
`
`3d
`
`Ar
`CsH,
`
`2-FC6H4
`3-FCeH4
`
`4-FCeH4
`
`2,5-F,CcHq
`
`mPb
`178-179
`
`193-195
`163-165
`
`188-190
`
`177-178
`
`a " "
`
`MES'
`EDSO
`10.3
`(9.1-11.6)
`e
`40.0
`136
`13.3
`(115-162)
`(11.5-15.3)
`144
`12.7
`(123-171)
`(10.4-15.1)
`e
`23.8
`(20.2-28.4)
`e
`2.6-FOC.H,
`>25. <lo0
`3e
`237-239
`,
`The compounds were administered intraperitoneally. EDw and
`TD,, values are in mg/kg. Numbers in parentheses are 95% con-
`fidence intervals. bMelting points ("C) and uncorrected. 'MES =
`maximal electroshock seizure test. d T o ~ = neurologic toxicity de-
`termined from horizontal screen. e Not determined.
`selected for synthesis, the a-substituent was systematically
`varied. Both aromatic (2c-f) and heteroaromatic (2g-p)
`moieties were incorporated into the amino acid backbone.
`In all cases, the functionalized amino acid racemates were
`prepared and tested.
`The pharmacological properties observed for 2g war-
`ranted further investigation of this compound. Accord-
`ingly, two different types of structural modifications of the
`N-terminal benzyl moiety were made. First, a series of
`racemic fluorine-substituted benzylamides 3a-e were
`synthesized (Table 11). Impetus for this study was pro-
`vided by an earlier observation that a modest improvement
`of the overall activity of 2a in mice (ip) was obtained upon
`incorporation of a fluorine atom at the meta position of
`the aromatic ring.3 The second structural modification
`examined for 2g involved the replacement of the N -
`benzylamide group by the corresponding N-a-methyl-
`benzylamides. Use of (R)-a-methylbenzylamine and
`(S)-a-methylbenzylamine in the synthesis permitted the
`preparation and pharmacological evaluation of each of the
`four individual diastereomers of 4.
`
`
`
`H
`
`0 O
`4
`The final group of drug candidates synthesized were the
`individual E(-) and S-(+) stereoisomers of 2g (Table 111).
`The marked selectivity previously noted1v4p5 for the indi-
`vidual enantiomers of 2a and 2b prompted this investi-
`gation.
`
`Table 111. Selected Physical and Pharmacological Data in Mice
`for Functionalized Amino Acid Stereoisomers
`
`Kohn et al.
`
`R2
`ir
`if
`C ~ c N H C H C N K C H 2 - ~
`0
`0
`
`
`toxd
`TDw
`-40
`
`no.
`(R,S)-2g
`
`R*
`2-furanyl
`
`mPb
`178-179
`
`2-furanyl
`
`196-197
`
`2-furanyl
`CH3
`
`CH3
`
`CH3
`
`C6H5
`
`196-197
`139-141
`
`139-141
`
`139-142
`
`2 0 2 - 2 0 3
`
`219-221
`
`MESc
`EDw
`10.3
`(9.1-11.6)
`23.8
`3.3
`(2.8-3.9)
`> 200
`>25
`454
`76.5
`(417-501)
`(66.6-89.0)
`214
`54.8
`(148-262)
`(50.3-59.7)
`84 1
`548
`(691-954)
`(463-741)
`>40
`32.1
`(27.5-40.2)
`>so
`26.4
`C6H5
`(21.1-32.0)
`> 300
`>loo. <300
`CcH,
`221-222
`
`,
`.
`" "
`The compounds were administered intraperitoneally. EDw and
`TD, values are in mg/kg. Numbers in parentheses are 95% con-
`fidence intervals. bMelting points ("C) are uncorrected. MES =
`maximal electroshock seizure test. Tox = neurologic toxicity de-
`termined from horizontal screen. eValues determined at the Epi-
`lepsy Branch, NINCD, NIH; see ref 4. The median toxic dose
`(TD,) was determined by using the rotorod test (see: Durham, N.
`W.; Miya, T. S. J. Am. Pharm. Assoc. 1957,46, 208). fReference 4.
`
`Scheme 1. Preparation of Compound 1 via the Mixed Carbonic
`Anhydride Method
`
`amine
`
`H
`
`B
`
`H
`2
`
`R3NH2
`
`Chemistry
`The strategies employed in the synthesis of the func-
`tionalized amino acid derivatives were patterned after
`procedures previously employed. The preparation of
`compounds Zc-e,g-i,k,l,n-p have been r e p ~ r t e d . ~ In-
`troduction of the aromatic or heteroaromatic group at
`carbon 2 in compounds 2c-e,g-l,n-p was accomplished by
`an amidoalkylation reaction using 2-acetamido-N-
`benzyl-2-ethoxyacetamide (5), BF3, and the appropriate
`aromatic substrate. The reactions proceeded in moderate
`yields (28-67 %) with excellent regioselectivity.
`
`II
`
`(6) For the pharmacological properties of the related a,a-di-
`alkyl-a-phthalimidoacetamides and apdialkyl-a-benzamido-
`acetamides, see: Upham, S. D.; Dermer, 0. C. J. Org. Chem.
`1957, 22, 799.
`(7) Porter, R. J.; Cereghino, J. J.; Gladding, G. D.; Hessie, B. J.;
`Kupferberg, H. J.; Scoville, B.; White, B. G. Cleveland Clin.
`Q. 1984,51, 293.
`(8) Eudismic ratio = ratio of activities of the two enantiomers.
`See: Lehmann, P. A. Trends Pharmacol. Sci. 1982, 3, 103.
`
`H O
`5
`The remaining compounds in this study were prepared
`by the mixed carbonic anhydride method (Scheme 1).lo In
`
`(9) LeCall, P.; Sawhney, K. N.; Conley, J. D.; Kohn, H. Znt. J.
`Pept. Protein Res. 1988, 32, 279.
`
`IPR2014-01126- Exhibit 1022 p. 2
`
`

`
`a-Aromatic and a-Heteroaromatic Amino Acids
`
`Journal of Medicinal Chemistry, 1990, Vol. 33, No. 3 921
`
`Scheme 11. Improved Procedure for the Preparation of
`(R,S)-a-Acetamido-2-furanacetic Acid (10)
`0
`0
`
`II
`CHJNHC~CmH,CH,
`- 1 1
`
`0 B r o
`Cb!Nk&YC&
`
`12
`
`Br,
`[AIBN1
`CCI,
`hv
`
`ZnCl,
`
`1. KOH/9O%EtOH
`
`u
`1Q
`this procedure, the N-acylated amino acid 6 was treated
`with an alkyl chloroformate in the presence of a tertiary
`amine to generate the mixed N-acyl amino acid carbonic
`ester anhydride 7. This intermediate was not isolated but
`reacted in situ with the appropriate amine (R3NH2) to
`produce the N-acyl amino acid N-substituted amide 1.
`The starting N-acylated amino acid selected for the syn-
`thesis of 2f was N-t-Boc-(R,S)-2-naphthy1glycine1l (8).
`
`8 .p
`
`CY 0
`cH~-L-O-!NH-C-C-OH
`I II
`I
`H 0
`C Y
`
`CH,!NH-
`
`-C-OH
`I II
`H O
`9
`B
`Subsequent removal (CF3C02H) of the N-protecting group
`after the mixed carbonic anhydride coupling step, followed
`by acetylation with acetyl chloride and triethylamine,
`yielded 2f. In the synthesis of (R,S)-2g, (R)-2g, (S)-2g, 2m,
`3, and 4 the appropriate N-acetyl amino acid was directly
`employed, thereby simplifying the experimental procedure.
`Synthesis of (R,S)-a-acetamido-3-thiopheneacetic acid (9)
`was readily accomplished beginning with (R,S)-a-amino-
`3-thiopheneacetic acid and acetic anhydride. An improved
`procedure (Scheme 11) was developed for the synthesis of
`(R,S)-a-acetamido-2-furanacetic acid (10). This func-
`tionalized amino acid served as the starting material for
`compounds 2g, 3, and 4. The method adopted took ad-
`vantage of the recent report on the employment of pro-
`tected a-bromo amino acid derivatives as electrophilic
`glycine templates in amino acid synthesis.I2 Accordingly,
`ethyl acetamid0-2-bromoacetate'~ (12) was prepared from
`ethyl acetamidoacetate (1 1) and then treated with furan
`and ZnC12 to give 13. Hydrolysis of the ethyl ester yielded
`10, the necessary precursor for the mixed carbonic anhy-
`dride coupling procedure (Scheme I). The overall yield
`for 10 in this three-step sequence was 65%.
`Several different alkyl chloroformates and tertiary
`amines were examined for the mixed carbonic anhydride
`reaction beginning with 10. Higher conversion rates were
`generally obtained with isobutyl chloroformate and 4-
`methylmorpholine.10 The yields for the final coupling step
`
`Figure 1. ORTEP view of compound (R)-2g with atom labeling
`scheme. The thermal ellipsoids are 20% equiprobability enve-
`lopes, with hydrogens as spheres of arbitrary diameter. Only one
`orientation of the disordered phenyl ring is shown.
`for the preparation of the fluorine-substituted aryl amides
`3 (Table 11) ranged from 50 to 88%. A comparable syn-
`thetic protocol was adopted for methylbenzyl amides 4.
`The configuration at C-2 in each of the four individual
`diastereomers of 4 was not determined.
`Synthesis of the two enantiomeric forms of 2g, (R)-2g,
`and (S)-2g (Table 111) was achieved by resolution of ra-
`cemic 10 via fractional recrystallization of the diastereo-
`meric salta formed with (R)- and (S)-a-methylbenzylamine,
`respectively, and then coupling the individual stereoiso-
`men with benzylamine. Use of isobutyl chloroformate and
`4-methylmorpholine in the mixed carbonic anhydride
`coupling procedure did not lead to significant amounts of
`racemization of 2g. An X-ray crystallographic structural
`determination of (R)-2g was conducted to provide basic
`information concerning the solid-state structure of this
`compound, and the ORTEP view is presented in Figure 1.
`Thermal disorder limited the amount of data obtainable
`in this determination, but some useful observations con-
`cerning the structure of the molecular backbone of (R)-2g
`in the solid state can still be made. Significant double
`bond character in the C-N peptide linkages were indicated
`by unusually short Nl-C2 (1.338 (9) A) and N2-C4 (1.323
`(8) A) bond lengths and unusually long Cl-C2 (1.509 (9)
`A) and C3-C4 (1.534 (8) A) bond lengths [for C(sp2)-C-
`(sp3)]. Comparable observations have been previously
`noted in related c ~ m p o u n d s . ~ ~ The torsion angles about
`N 1 4 2 and N 2 4 4 are essentially O', as would be expected
`in this highly conjugated system, and the sum of the angles
`about both nitrogens is 359', indicating virtual planarity
`and substantial delocalization of the lone electron pairs.
`The absolute configurations of the enantiomers of 10
`were determined by converting an enriched sample of
`(R)-10 to the corresponding methyl ester (R)-14 with
`diazomethane. The optical rotation observed for this ad-
`duct
`= -95'
`(c = 1, MeOH)] was comparable to a
`sample obhned after treatment of racemic 149 with papain
`
`5 0
`CbCNH HCOCH,
`II
`II
`0
`0
`
`
`(10) For an excellent discussion and review of this method, see:
`Anderson, G. W.; Zimmerman, J. E.; Callahan, F. M. J. Am.
`Chem. SOC. 1967,89, 5012.
`(11) Kukolja, S.; Draheim, S. E.; Pfeil, J. L.; Cooper, R. D. G.;
`Graves, B. J.; Holmes, R. E.; Neel, D. A,; Huffman, G. W.;
`Webber, J. A.; Kinneck, M. D.; Vasileff, R. T.; Foster, B. J. J.
`Med. Chem. 1985,28, 1886.
`(12) Williams, R. M.; Sinclair, P. J.; Zhai, D.; Chen, D. J. Am.
`Chem. SOC. 1988,110, 1547.
`(13) Kuber, R.; Steglich, W. Liebigs Ann. Chem. 1983, 599.
`
`L4
`in aqueous DMF. This enzymatic system has been re-
`
`(14) (a) Ishida, T.; Tanabe, N.; Inoue, M. Acta Crystallogr. 1983,
`C39, 110. (b) Kojima, T.; Tanaka, I.; Ashida, T. Zbid. 1982,
`B38, 221. (c) Hansen, L. K.; Hagen, E. A.; Loennechen, T.;
`Aasen, A. J. Acta Chem. Scand. 1982, B36,327. (d) Aubry, A.;
`Vitoux, B.; Boussard, G.; Marraud, M. Znt. J. Pept. Protein
`Res. 1981, 18, 195 and references therein.
`
`IPR2014-01126- Exhibit 1022 p. 3
`
`

`
`922 Journal of Medicinal Chemistry, 1990, Vol. 33, No. 3
`ported to selectively hydrolyze racemic N-protected fu-
`rylglycine methyl esters to the free @)-acids and unreacted
`@)-esters in high enantiomeric excess.15
`Several attempts were conducted to directly employ
`chiral (R)-13 or (R)-14 (obtained by papain-mediated hy-
`drolysis of the corresponding racemic esters) for the
`preparation of (R)-2g. Unfortunately, treatment of either
`ester with benzylamine in the absence or presence of
`NaCN gave racemic 2g.16
`Pharmacological Evaluation
`The N-acetyl amino acid N-substituted amides 2-4 were
`tested for anticonvulsant activity by using the procedures
`described by Krall et al." All compounds were admin-
`istered intraperitoneally (ip) in mice. Tables 1-111 list the
`median effective dose (ED,) values required to prevent
`seizures in the MES test by racemic 2, racemic 3, and the
`individual enantiomers of 2g, respectively. Included in
`these tables are the median toxic dose (TDW) values de-
`termined for select compounds by using the horizontal
`screen test.18
`Table I lists the pharmacological data for those com-
`pounds in which only the a-carbon moiety has been
`modified. Evaluation of this subset of results revealed
`several important observations. First, addition of elec-
`tron-releasing hydroxy (Le., 2c and 2e) or methoxy (i.e.,
`2d) groups to the a-substituted phenyl group in 2b or
`expansion of the aromatic ring from the phenyl group in
`2b to the naphthyl residue in 2f led to a precipitous drop
`in anticonvulsant potency. Second, replacement of the
`a-phenyl ring in 2b with an electron-rich, five-membered
`heteroaromatic ring resulted in a substantial improvement
`in the potency of the compound in the MES test. Notable
`protection against seizures were observed for the racemates
`of 2g-j and 21. The ED,, values for these compounds
`compared favorably with the reported data for phenytoin.'
`Third, placement of a methyl substituent on the five-
`membered heteroaromatic ring was accompanied by a
`decrease in the potency of the drug candidate versus the
`unsubstituted compounds (i.e., 2h versus 2g; 2j, 2k versus
`2i). Fourth, replacement of the a-heteroaromatic sub-
`stituent by the corresponding benzoheteroaromatic group
`led to a reduction in biological activity (i.e., 2n-p). This
`observation paralleled the results obtained for 2b versus
`2f.
`The second and third series of compounds tested for
`anticonvulsant activity were adducts in which the terminal
`N-benzylamide moiety in 2g was altered. Table 11 lists the
`comparative data obtained for five fluorine-substituted
`derivatives. All the compounds exhibited pronounced
`activity in the MES test. The meta (3b) and para (3c)
`fluoro adducts displayed activities comparable to that of
`2g, while a small reduction in activity versus 2g was noted
`for ortho derivative 3a, and the two difluoro analogues 3d
`and 3e. These data contrasted with the pharmacological
`results secured from the a-methylbenzylamides 4a-d.
`Increasing the size of the benzylamide moiety by incor-
`poration of an a-methyl group resulted in a significant
`decrease in the anticonvulsant potency of the drug can-
`didate regardless of the stereochemical relationship be-
`tween the two asymmetric centers. The MES EDm values
`
`(15) Drueckhanmer, D. G.; Barbas, C. F.; Nozaki, K.; Wong, C.-H.;
`Wood, C. Y.; Ciufolini, M. A. J. Org. Chem. 1988, 53, 1607.
`(16) Hogberg, T.; Strom, P.; Ebner, M.; Ramsby, S. J. Org. Chem.
`1987,52, 2033.
`(17) Krall, R. L.; Penry, J. K.; White, B. G.; Kupferberg, H. J.;
`Swinyard, E. A. Epilepsia 1978,19, 409.
`(18) Coughenour, L. L.; McLean, R. R.; Parker, R. B. Pharmacol.
`Biochem. Behav. 1977,6, 351.
`
`Kohn et al.
`for these compounds were all greater than 100 mg/kg. A
`similar trend was previously noted in the 2-acetamido-N-
`benzylpropionamide (2a) ~ e r i e s . ~
`Table I11 lists the pharmacological data for the two
`individual isomers of 2g along with the racemic mixture,
`as well as the corresponding data for 2a and 2b.4 In all
`three series of compounds a pronounced improvement in
`anticonvulsant potency was noted for the R enantiomer
`versus either the S isomer or the racemate. Moreover, in
`each case little activity in the MES test was observed for
`the S enantiomer. The ED50 value of (R)-2g was 3.3
`mg/kg, which was considerably lower than that reported
`for phenytoin' (EDm = 9.5 mg/kg). The enhanced potency
`of (R)-2g contributed to the observed high protective index
`= 7.2) for this compound, which compared
`(TD,/ED,
`favorably with the value observed for phenytoin (TDw/
`ED50 = 6.9).
`Conclusions
`The pharmacological data obtained in this investigation
`significantly extended the structure-activity profile pre-
`viously reported for functionalized amino acid deriva-
`
`t i v e ~ . ~ ~ ~ The observed data supported our hypothesis that
`stringent steric and electronic requirements exist for
`maximal anticonvulsant activity in this novel class of
` compound^.^ The outstanding potencies noted for 2g and
`2i in the MES test suggested that the placement of rela-
`tively small, electron-rich groups at the a-position in 1 was
`beneficial for anticonvulsant activity. Furthermore, our
`finding that the primary activity of 2g resided in the R
`enantiomer provided additional evidence for the marked
`stereospecificity exhibited in this new class of anticon-
`vulsants. Additional studies are in progress investigating
`the generality of this class of compounds as well as their
`mode of action.
`Experimental Section
`Chemistry. General Methods. Melting points were deter-
`mined with a Thomas-Hoover melting point apparatus and are
`uncorrected. Infrared spectra (lR) were run on Perkin-Elmer 1330
`and 283 spectrometers and calibrated against the 1601 cm-' band
`of polystyrene. Absorption values are expressed in wavenumben
`(cm-'). Proton ('H NMR) and carbon (13C NMR) nuclear mag-
`netic resonance spectra were taken on Nicolet "-300
`and General
`Electric QE-300 NMR instruments. Chemical shifts (6) are in
`parts per million (ppm) relative to MelSi and coupling constants
`(J values) are in hertz. Low-resolution mass spectra (MS) were
`recorded at an ionizing voltage of 70 eV with a Varian MAT CH-5
`spectrometer at the Lilly Research Laboratories. Microanalyses
`were provided by the Physical Chemistry Department of the Lilly
`Research Laboratories. Thin- and thick-layer chromatography
`were run on precoated silica gel GHLF microscope slides (2.5 X
`10 cm; Analtech No. 21521) or silica gel GHLF (20 X 20 cm;
`Analtech 11187).
`Preparation of ( R ,S )-2-Acetamido-N-benzyl-2-(5-
`methylpyrroly1)acetamide (2j). 2-Acetamido-N-benzyl-2-eth-
`oxyacetamides (5,2.00 g, 8 mmol) was suspended in anhydrous
`EhO (175 mL), and then BF,.EhO (1.38 g, 9.7 mmol) was added
`and the resulting solution was stirred (15 min). 2-Methylpy~ole'~
`(0.85 g, 10 mmol) was then added and the reaction mixture was
`stirred under Nz (6 days), during which time the color of the
`reaction mixture turned reddish brown and a dark-brown deposit
`formed at the bottom of the flask. The clear solution was decanted
`and treated with an aqueous saturated NaHC03 solution con-
`taining ice (100 mL) for 30 min. The aqueous reaction mixture
`was extracted with EtOAc (3 X 30 mL). The combined extracts
`were dried (Na#Or), and the solvent was removed in vacuo. The
`brown oily residue was purified by flash column chromatography
`using 2% MeOH/CHCI, as the eluent to yield 0.20 g (9%) of the
`
`(19) Castro, A. J.; Deck, J. F.; Hugo, M. T.; Marsh, J. P.; Pfiffer,
`R. J. J . Org. Chem. 1963, 28, 857.
`
`IPR2014-01126- Exhibit 1022 p. 4
`
`

`
`a-Aromatic and a-Heteroaromatic Amino Acids
`
`Journal of Medicinal Chemistry, 1990, Vol. 33, No. 3 923
`
`the reaction solution with concentrated HCl (pH 1,15 mL) led
`desired product. Compound 2j was recrystallized from ethyl
`to the formation of a precipitate. The mixture was filtered and
`acetate/hexane to give a light yellow amorphous solid: R, 0.44
`(955, CHC13/MeOH); mp 167-168 "C; IR (KBr) 3250,1630,1520,
`the collected white solid was recrystallized from 1:l 95%
`1420, 1360, 1300, 1260, 1230, 1160, 1110, 1020 cm-';
`'H NMR
`EtOH/H20, producing light yellow crystals: yield 3.55 g (75%);
`mp 190-192 "C; 'H NMR (DMSO-d6) 6 1.90 (s,3 H), 5.42 (d, J
`(DMSO-d,) 6 1.87 (8, 3 H), 2.13 (8, 3 H), 4.27 (br s, 2 H), 5.33 (d,
`= 7.6 Hz, 1 H), 7.13 (d, J = 5.0 Hz, 1 H), 7.50-7.55 (m, 2 H), 8.69
`J = 7.4 Hz, 1 H), 5.60 (s, 1 H), 5.77 (8, 1 H), 7.19-7.30 (m, 5 H),
`8.22 (d, J = 7.4 Hz, 1 H), 8.45 (t, J = 5.5 Hz, 1 H), 10.38 (s, 1 H);
`(d, J = 7.6 Hz, 1 H), 12.89 (8, 1 H); "C NMR (DMSO-de) 22.3,
`"C NMR (DMs0-d~) 12.74, 22.49, 42.11, 51.21, 105.09, 106.07,
`52.2, 123.3, 126.5, 127.2, 137.3, 169.3, 171.8 ppm. Anal. (CBH9-
`126.16, 126.64, 126.85, 127.09 (2 C), 128.17 (2 C), 139.33, 168.88,
`NOSS) C, H, N.
`(R,S)-a-Acetamido-N-benzyl-3-thiopheneac (2m).
`169.79 ppm. Anal. (C16H&302) C, H, N.
`Preparation of (R,S)-2-Acetamido-N-benzyl-2-(2-
`With the procedure previously described for the preparation of
`naphthy1)aoetamide (20. N-t-Boc-(R,S)-2-naphthylglycine
`N-t-Boc-(R,S)-2-naphthylglycine N-benzylamide, compound 9
`
`N-Benzylamide. N-t-Boc-(R,S)-2-11aphthylglycine~~ (8,7.53 g,
`(2.99 g, 15 mmol) was treated with ESN (1.51 g, 2.10 mL, 15 "01)
`25 mmol) was combined with CH&N (100 mL) and the mixture
`and ethyl chloroformate (1.63 g, 1.43 mL, 15 mmol) and benz-
`was placed into an ice/salt water bath (-5 "C). ESN (2.53 g, 3.50
`ylamine (1.77 g, 16.5 mmol). The filtrate upon workup was
`mL, 25 mmol) was added dropwise, followed by ethyl chloro-
`Concentrated in vacuo and the resulting yellow solid was re-
`formate (2.71 g, 2.40 mL, 25 m o l ) . All additions were done slowly
`crystallized from 1:l 95% EtOH/H20: yield 1.91 g (44%); mp
`so that the temperature of the mixture did not rise above 0 OC.
`198-199 OC; IR (KBr) 3460,1675,1570,1400,720,695 cm-'; 'H
`NMR (DMSO-de) 6 1.91 (8, 3 H), 4.29 (d, J = 5.2 Hz, 2 H), 5.61
`The mixture was then stirred at -5 "C (20 min). Benzylamine
`(d, J = 7.9 Hz, 1 H), 7.14-7.50 (m, 8 H), 8.55 (d, J = 7.9 Hz, 1
`(2.95 g, 3.0 mL, 27.5 mmol) in CH3CN (10 mL) was added dropwise
`H), 8.74 (t, J = 5.2 Hz, 1 H); '3C NMR (DMSO-dJ 22.3,42.0,52.5,
`and the mixture was stirred at -5 "C (1 h) and then room tem-
`perature (18 h). The brown mixture was concentrated in vacuo
`122.4, 126.1, 126.7, 127.0 (3 C), 128.2 (2 C), 139.0, 139.2, 169.0,
`and the residue was combined with hot THF and cooled in the
`169.8 ppm. And. (C&leN202S) C, H, N.
`Synthesis of (R,S)-Ethyl a-Acetamido-2-furanacetate (13).
`freezer (3 h), resulting in the formation of a white precipitate.
`The mixture was filtered and the precipitate was collected, dried
`An ethereal solution of ZnC12 (1 N, 28.00 mL, 0.028 mol) was added
`in vacuo, and identified as EhNHC1. The fitrate was concentrated
`to a stirred solution of 1213 (4.40 g, 0.019 mol) and furan (11.23
`g, 0.165 mol) in dry THF (100 mL), and allowed to stir at room
`in vacuo and the resulting solid was recrystallized from chloro-
`form/hexane: yield 4.18 g (43%); mp 127-129 "C; IR (KBr) 3240,
`temperature (5 h). The mixture was then treated with H20 (50
`1635,1520,1505,1460,1370,720,705 cm-'; 'H NMR (DMSO-d6)
`mL), the organic phase was separated, and the aqueous layer was
`6 1.31 (8, 9 H), 4.32 (9, 2 H), 5.42 (9, 1 H), 7.14-7.79 (I& 12 H),
`extracted with CHzC12 (2 x 100 mL). The organic layers were
`the N-H protons were not detected; 13C NMR (DMSO-d,) 28.2
`combined and dried (Na2S04), and the volatile materials were
`(3C), 43.3, 58.3, 80.0, 124.6, 126.1, 126.2, 126.3, 127.1, 127.2 (2 C),
`removed by distillation in vacuo to give approximately 4.00 g
`127.5, 127.9, 128.3 (2 C), 128.6, 133.0, 133.2, 135.9, 137.7, 155.3,
`(97%) of light-brown semisolid material. TLC analysis showed
`a major spot at R, 0.30 (1% MeOH/CHC13). The desired com-
`170.3 ppm. Anal. (CuHzeN203) C, H, N.
`pound was purified by flash column chromatography on silica gel
`(R,S)-2-Naphthylglycine N-Benzylamide Methane-
`sulfonate. The Boc-protected amino acid N-benzylamide (3.91
`using 1% MeOH/CHC13 as the eluent to give 3.60 g (87%) of a
`beige solid mp 68-70 "C (lit? mp 69-70 "C).
`g, 10 mmol) was dissolved in trifluoroacetic acid (25 mL) and was
`Preparation of (R,S)-a-Acetamido-2-furanacetic Acid (10).
`stirred at room temperature (30 min), during which time gas
`evolved. The solution was concentrated in vacuo and the residue
`Compound 13 (4.00 g, 19 mmol) was dissolved in 9O:lO EtOH/H20
`was redissolved in MeOH (50 mL). Methanesulfonic acid (0.96
`(150 mL) and then KOH (2.00 g, 35 mmol) was added and the
`g, 0.65 mL, 10 mmol) was added dropwise and stirred (5 min).
`resulting solution was stirred at room temperature (48 h). The
`After concentrating the solution in vacuo, the residue was re-
`reaction was concentrated in vacuo and the residue was diluted
`with HzO and then washed with Et20 (3 X 50 mL). The aqueous
`peatedly dissolved in MeOH and the solvent was removed (3 x
`50 mL). The residue was then dried under vacuum (18 h), leaving
`layer was then made acidic with 8.5% H3P04 and extracted with
`a yellow oil. Trituration with CH2C12 gave a white solid: yield
`EtOAc (3 X 150 mL). The organic layers were combined, dried
`2.48 g (83%); mp 180-182 "C; IR (KBr) 3245,1655,1460,1385,
`(Na2S04), and evaporated to dryness in vacuo to give 10: yield
`730,700 cm-'; 'H NMR (DMSO-d6) 6 2.35 (s,3 H), 4.33 (d, J =
`2.65 g (76%), mp 172-174 "C (lit? mp 171-172 "C); R,0.37 (8l:l
`5.5 Hz, 2 H), 5.18 (8, 1 H), 7.15-8.09 (m, 12 H), 8.78 (8, 1 H), 9.06
`2-propanol/NH40H/H20).
`Synthesis of (R $3)-a-Acetamido-N-benzyl-substituted-
`(t, J = 5.5 Hz, 1 H); "C NMR (DMs0-d~) 39.5,42.3, 55.7, 124.8,
`126.6, 126.7, 127.0, 127.5, 127.8, 128.0 (2 C), 128.3, 131.4, 132.4,
`2-furanacetamides (2-4). General Procedure. 4-Methyl-
`132.8, 138.3, 167.1 ppm. The resonances for the remaining aro-
`morpholine (1 equiv) was added to a solution of 10 (1 equiv) in
`matic carbons were not detected. Anal. (CaaN204S) C, H, N.
`dry THF (75 mL/10 mmol) at -10 to -15 "C under N1. After
`(R ,S)-2-Acetamido-N-benzyl-2-(2-naphthyl)acetamide
`stirring (2 min), isobutyl chloroformate (1 equiv) was added,
`(20. (R,S)-2-Naphthylglycine N-benzylamide methanesulfonate
`leading to the precipitation of a white solid. The reaction was
`(1.59 g, 4.1 mmol) was suspended in CH3CN (25 mL) and was then
`allowed to proceed for two additional minutes and then a solution
`of the substituted benzylamine (1 equiv) in THF (10 mL/10 mmol)
`cooled in an ice bath. ESN (0.83 g, 1.20 mL, 8.2 mmol) was added
`was added over 5 min at -10 to -15 "C. The reaction mixture
`dropwise, followed by acetyl chloride (0.32 g, 0.30 mL, 4.1 mmol).
`was allowed to stir at room temperature for 5 min and then the
`The ice bath was removed and stirring was continued at room
`temperature (18 h). The solution was concentrated in vacuo and
`4-methylmorpholine hydrochloride salt was filtered. The organic
`the residue was recrystallized from 1:l 95% EtOH/H20: yield
`layer was concentrated in vacuo, the residue was triturated with
`1.31 g (95%); mp 210-211 OC; IR (KBr) 3230,1710,1625,1535,
`EtOAc, and the remaining white solid was fitered. Concentration
`1465,760,710 cm-'; 'H NMR (DMSO-d6) 6 1.94 (e, 3 H), 4.30 (d,
`of the EtOAc layer led to additional amounts of the white solid.
`J = 5.2 Hz, 2 H), 5.86 (d, J = 7.9 Hz, 1 H), 7.15-7.91 (m, 12 H),
`The desired product was purified by recrystallization or flash
`8.63 (d, J = 7.9 Hz, 1 H), 8.33 (t, J = 5.2 Hz, 1 H); 13C NMR
`chromatography of the combined solid material.
`(DMSO-de) 22.5,42.2, 56.6, 125.5,126.0, 126.1,126.3, 126.8,127.1
`Using this procedure the following compounds were prepared.
`(R,S)-a-Acetamido-N-benzyl-2-furanacetamide
`(2 C), 127.5, 127.7, 127.9, 128.2 (2 C), 132.4, 132.8, 136.5, 139.1,
`(2g).
`Using benzylamine (0.27 g, 2.56 mmol) and racemic 10 (0.47 g,
`169.2,170.0 ppm. Anal. (Cz1H20N20z) C, H, N.
`P r e p a r a t i o n of (R,S)-a-Acetamido-N-benzyl-3-
`2.56 mmol) gave 0.46 g (65%) of 2g. The product was recrys-
`(R ,S )-a-Acetamido-3-
`thiopheneacetamide
`(2m).
`tallized from EtOAc to give a white solid mp 177-178 OC (lit?
`thiopheneacetic Acid (9). (R,S)-a-Amino-3-thiopheneacetic acid
`mp 178-179 "C); R, 0.30 (2% MeOH/CHC13); 'H NMR
`(DMSO-de) 6 1.90 (8, 3 H), 4.31 (d, J = 6.0 Hz, 2 H), 5.58 (d, J