3350
`
`Med Chem 1993 36 33503360
`
`Synthesis and Anticonvulsant Activities of a-Heterocyclic
`a-Acetamido-N-benzylacetamide
`Derivatives
`
`Harold Kohnt Kailash
`
`Sawhneyt Patrick Bardelt David
`
`RobertsonU and
`
`David Leander
`
`Department of Chemistry University of Houston Houston Texas 77204-5641 and Lilly Research Laboratories
`Eli Lilly and Company Lilly Corporate Center Indianapolis Indiana 46285
`
`Received May 14 1993
`
`containing
`
`five- and six
`
`Earlier studies showed that RS-a-acetamido-N-benzylacetamides
`membered aromatic or heteroaromatic group appended at the Ca site displayed outstanding
`seizure MES test
`in mice An expanded set of
`activity in the maximal electroshock-induced
`The observed findings
`have been prepared and evaluated
`Ca-heteroaromatic
`analogues of
`extended the structureactivity relationships previously discerned for this novel class of anti
`a-oxazol-2-yl 18 and
`convulsants and have validated previous trends The a-furan-2-yl
`afforded excellent protection against MES
`cr-thiazol-2-yl 19 a-acetamido-N-benzylacetaniides
`induced seizures in mice The ED50 and P1 values for these adducts rivaled those reported for
`phenytoin The outstanding properties provided by
`led to an in-depth examination of the effect
`The
`of structural modification at key sites within this compound
`on biological activity
`data in this series indicated that stringent steric and electronic requirements
`pharmacological
`existed for maximal activity and revealed the outstanding activity of R--a-acetamido-N-4-
`fluorobenzyl-a-furan-2-ylacetaniide
`
`occurring amino acid derivatives con-
`Non-naturally
`stitute an increasing resource of new chemotherapeutic
`and CNS agents and
`agents that include antibacterial
`enzyme inhibitors In recent years we have reported on
`the anticonvulsant properties of functionalized amino acid
`Our studies demonstrated that a-acet-
`derivatives
`five- and six-
`amido-N-benzylacetamides 2containing
`membered aromatic or heteroaromatic group appended
`at the Ca-site afforded excellent protection against
`maximal electroshock MES induced seizures
`in mice
`36 For example the ED50 values against MES
`Table
`32.1 mg/kg and
`seizures for the racemic a-phenyl
`10.3 mg/kg derivatives6 compared ff
`ct-furan-2-yl
`vorably with phenobarbital 21.8 mg/kg and phenytoin
`9.5 mg/kg.8 Examinationof the individual enantiomers
`of and demonstrated the importance of stereochemistry
`at the Ccr site in on biological activity.56 In both
`and
`stereoisomer was 10 times more potent
`the
`in the
`control of MES seizures than the Senantiorner This
`difference in activity is the greatest eudismic ratio retorted
`to date for MES-selective anticonvulsant agents
`
`R1NH
`
`CNHR3
`
`CH3NH
`
`LNHCHS__Q
`
`In the present study we report
`the synthesis and
`carefully selected series of
`pharmacological activities of
`Ccr-heteroaromatic analogues of
`Information is pro-
`vided on the effect of type number and site of heteroatom
`substitution within the Ca-substituent onanticonvulsant
`The outstanding properties provided
`activity Table
`
`correspondence
`
`shouid be addressed
`
`at
`
`the
`
`University of Houston
`tUniversity of Houston
`iLffly Research Laboratories
`
`9393 Towne Center Dr
`
`Abstract published in Advance ACS Abstracts October
`
`1993
`
`by a-acetamido-N-benzyl-a-furan-2-ylacetamide
`against MES seizures led to an in-depth examination of
`on
`the effect of structural modification at key sites in
`biological activity Table II
`Included in this study was
`also the preparation of several enantiopure congeners of
`R-4 to demonstrate that
`this absolute configuration
`afforded compounds with marked anticonvulsant activity
`
`Selection of Compounds
`
`Our investigation proceeded
`in two stages First we
`determined the effect of the Ca-heteroaromatic group
`Amino acid
`on anticonvulsant activity Table
`in
`served as the reference com
`derivatives 486 Table
`pounds for this investigation The placement of additional
`heteroatoms within these derivatives or the preparation
`of isomeric adducts led to multiple effects These included
`perturbations in the electron density of the aromatic ring
`changes
`the nonbonding
`in the spatial orientation of
`electrons and alterations in the basicity and bioavailability
`of the drug candidates
`These multifaceted electronic
`structural and physical effects complicated the interpre
`tation of the biological data Nonetheless the pronounced
`in MES-induced seizure protection previ
`improvement
`ously observed
`by the placement of an electron-rich
`i.e ED50
`aromatic ring at the Ca-site in
`32.1
`10.3 mg/kg
`ED50
`mg/kg versus
`ED50
`44.8 mg/
`kg versus
`ED50
`16.1 mg/kg versus
`ED50
`10.3
`mg/kg prompted us to provide additional documentation
`for this trend The compounds selected for synthesis and
`evaluation were grouped into three categories The first
`set i.e 912 included aza analogues of where the Ca
`
`carboncarbon
`heteroaromatic ring was appended by
`bond Compounds in this series were a-imidazolyl
`and
`10 a-triazolyl 11 and a-tetrazolyl 12 The second
`the isomeric Ca
`i.e 1317 encompassed
`category
`azaromatics where heteroaromatic attachment
`amino acid backbone occurred through
`nitrogencarbon
`bond Compounds evaluated were a-pyrrolyl 13 a-pyra
`zolyl 14 a-imidazolyl 15 a-triazolyl 16 and a-tet
`razolyl 17 adducts Finally the third category i.e 18
`
`to the
`
`Breckenridge Exhibit 1017
`Breckenridge v. Research Corporation Technologies, Inc.
`
`0022-2623/93/1836-3350$04.O0/0
`
`1993 American Chemical Society
`
`

`
`a-Acetamido-N-benzylacetamide
`
`Derivatives
`
`Journal of Medicinal Chemistry 1993 Vol 36 No 22
`
`3351
`
`Table
`
`Physical and Pharmacological Data in Mice for Ca-Heteroaromatic
`R20
`
`a-Acetamido-N-benzylacetamides
`
`II
`
`ii
`
`CH3CNHC-CNHCH2
`
`no
`
`R2
`
`...
`
`...4
`
`CH
`
`_4
`
`_4
`
`I.LN
`
`-N
`
`SN
`
`fN
`
`NN
`
`N\
`
`3/
`
`4/
`
`5/
`
`6/
`
`7/
`
`81
`
`10
`
`11
`
`12
`
`13
`
`14
`
`15
`
`16
`
`17
`
`18
`
`19
`
`20
`
`mpb
`
`202203
`
`178179
`
`174175
`
`179181
`
`167169
`
`198199
`
`228230
`
`188191 dec
`
`205207
`
`236238
`
`182184
`
`158160
`
`146148
`
`148148
`
`169171
`
`164166
`
`166167
`
`164166
`
`P1
`
`3.9
`
`HSd TD50
`40
`
`4O
`
`30 100
`
`30 100
`
`100
`
`MESC ED50
`
`32.1 27.540.2
`
`10.3 9.111.6
`
`16.1 13.219.9
`
`3O0
`
`44.8 38.951.4
`
`87.8 69.9150
`
`100
`
`100
`
`100
`
`30 100
`
`80.2 66.6100.6
`
`16.5 14.122.5
`
`100
`
`30 100
`
`300
`
`10.4 9.211.6
`
`38.6 33.846.0
`
`12.1 9.514.5
`
`69.1 61.678.6
`
`3.7
`
`5.7
`
`100 300
`
`phenytoin
`phenobarbital
`valproate
`The compounds were administered intraperitoneally
`ED50 and TD50 values are in milligrams per kilogram Number in parentheses are
`The dose effect data
`95% confidence intervals
`curve was generated for all compounds that displayed sufficient activity
`doseresponse
`time of peak effect
`19 which was obtained at 0.25
`except for compound
`for these compounds was obtained at 0.5
`Melting points
`are uncorrected MES maximal electroshock
`seizure test HS TD50
`toxicity determined from horizontal screen unless
`neurologic
`otherwise noted P1 protective index TD50/ED50
`Reference
`determined 1Neurologic toxicity determined using the rotorod test
`Reference
`
`9.5 8.110.4
`21.8 15.022.5
`272 247338
`
`65.5h 52.572.1
`69.0 62.872.9
`426 369-450
`
`6.9
`
`3.2
`
`1.6
`
`20 contained Ca-mixed heteroaromatic systems The
`three compounds prepared were a-oxazoiyl 18 a-thiazolyl
`19 and -124-oxadiazolyl 20 derivatives
`In all cases
`the functionalized amino acids were synthesized as the
`racemates
`The second phase of this study Table II
`focused on
`a-acetamido-N-benzyl-a-furan-2-ylacetamide
`the
`compound evaluated
`most active
`study
`in the initial
`Structural modifications were conducted at key sites in
`including the furan ring i.e 21 the Ca-position i.e
`22 the two amide carbonyl groups i.e 23 24 and the
`
`i.e 2529 to discern how these
`N-benzyl substituent
`changes influenced biological activity Moreover because
`of the substantial eudismic ratio observed with enanti
`omers of
`enantiopure R-isomers of several congeners
`in the present series were prepared i.e R-30R-32 to
`demonstrate that this absolute configuration afforded
`compounds with marked anticonvulsant activity
`
`Chemistry
`The novel a-heteroaromatic amino acid derivatives 920
`were prepared from either a-acetamido-N-benzyl-a-bro
`
`

`
`3352
`
`Journal of Medicinal Chemistry 1993 Vol 36 No 22
`
`Table
`
`Physical and Pharmacological
`
`Data in Mice for a-Acethamido-N-benzyl-a-furan-2-ylacetamide
`RaY
`IICH3CNHCC NHR
`
`Kohn et al
`
`Derivativesu
`
`nO
`
`Ra
`
`Rb
`
`..L
`.J
`_i
`
`_jf
`
`R-41
`
`S-4f
`
`21a
`
`21b
`
`22
`
`23
`
`24
`
`25
`
`26
`
`27
`
`28
`
`29
`
`CH2CSHS
`
`CH2C6H5
`
`CH2CSHS
`
`CH2C6H
`
`CH2C6H5
`
`Rb
`
`mpb
`
`178179
`
`MESC ED50
`
`10.3 9.111.6
`
`HS TD50
`40
`
`196197
`
`3.3 2.83.9
`
`196-197
`
`25
`
`23.8
`
`200
`
`159161
`
`51.7 44.459.9
`
`130132
`
`89.8 78.4103.4
`
`pje
`
`3.9
`
`7.2
`
`CH3
`
`CH2C6H5
`
`300
`
`CH2CGHS
`
`CH2CSHS
`
`CH2fN
`
`CH2-j
`
`7880
`
`18.4 15.922.0
`
`99-101
`
`172174
`
`168170
`
`159161
`
`100
`
`30
`
`100
`
`30
`
`210212
`
`100
`
`30
`
`R-30
`
`R-31
`
`R-32
`
`_4
`
`....i
`
`CH2--_-O
`NHf
`CHF
`CHOF
`
`CH2f--CH3
`
`CHZCF3
`
`226-228
`
`100
`
`188190
`
`12.7 10.415.1
`
`144 123171
`
`205207
`
`3.5 2.94.4
`
`14.4 7.328.9
`
`11.3
`
`4.1
`
`210212
`
`43.6 26.1143
`
`193195
`
`22.815.9-33.4
`
`9.5 8.110.4
`21.8 15.022.5
`272 247338
`ED50 and TD50 values are in milligrams per kilogram Numbers in parentheses are
`The compounds were administered intraperitoneally
`The dose effect data
`95% confidence intervals
`doseresponse
`curve was generated for all compounds that displayed sufficient activity
`time of peak effect except
`for these compounds was obtained at 0.5
`for compound 27 which was obtained at
`Melting points
`MES maximal electroshock seizure test Compound was suspended in 30% PEG HS TD50
`are uncorrected
`neurologic toxicity determined
`protective index TD50/ED50
`from horizontal screen unless otherwise noted
`P1
`Reference
`Not determined
`Thick oil Reference
`toxicity determined using the rotorod test
`
`6.9
`
`3.2
`
`1.6
`
`phenytoin
`phenobarbital
`valproate
`
`Neurologic
`
`65.51 52.572.1
`69.0 62.872.9
`4261 369-450
`
`moacetamide7 33 or a-acetamido-N-benzyl-a-cyano-
`acetamide9 34 Addition of
`tetrahydrofuran solution
`of the C2-lithio salt of 1-diethoxymethylimidazole
`35 to 33 prepared in situ afforded
`after workup
`treatment of 33 with triethylamine
`Correspondingly
`salt of 1-N
`followed by introduction
`of
`the lithio
`N-dimethylsulfamoylimidazole1 36 gave 37 which upon
`deprotection with acid furnished 10 The structure of 37
`has been tentatively
`as the C4-imidazole-
`assigned
`comparison of the NMR
`substituted derivative based on
`chemical shift values for 37 versus the parent heterocycle
`36 and 1-NN-dimethylsulfamoyl-4-methylimidazole
`38 Table III
`Compound 38 was prepared by the
`addition of dimethylsulfamoyl chloride to 4-methylim-
`idazole 39 in the presence of triethylamine NMR and
`anaiyses 01 tne cruue reaction mixture inrncateu tne
`presence of only one major compound and the structure
`sup
`was confirmed by X-ray crystallography Figure
`plementary material Select H3C NMR decoupling
`experiments on 38 provided the assignments listed in Table
`
`Table HI NMR Assignments
`
`for Substituted Imidazolesa
`
`NNR
`\J
`NMRb
`H5
`
`SC NMRC
`C4
`
`C5
`
`7.13
`
`7.56
`
`7.40
`
`7.32
`
`6.75
`
`7.47
`
`121.96
`
`130.45
`
`140.26
`
`138.85
`
`131.00
`
`130.5f
`
`121.96
`
`118.75
`
`115.50
`
`114.34
`
`118.18
`
`115.9
`
`compd no
`
`midazole
`
`36
`
`37
`
`38
`
`39
`
`H4
`
`7.13
`
`7.13
`
`7.09e
`
`All spectra were recorded in DMSO-d5 unless otherwise indicated
`5The number in each entry is the chemical shift value
`observed
`NMR spectra were recorded at 300
`in ppm relative to Me4Si
`MHz
`SC NMR spectra were obtained at 75 MHz
`Spectra taken
`in CDC13 Reference 12b Reference 12a
`
`III and permitted the assignments for the corresponding
`NMR resonances in 36 and 37 The
`NMR assignments
`
`

`
`a-Acetamido-N-benzylacetamide
`
`Deriuatives
`
`Journal of Medicinal Chemistry 1993 Vol 36 No 22
`
`3353
`
`Scheme
`
`Preparation of a-Acetamido-N-benzyl-a-methyl-a-furan-2-ylacetaniide
`
`22
`
`Br
`
`II
`
`CH3CNH __COCHS
`
`CH2
`
`HBr
`
`coo
`CHsCNH__C_NHCH2___Q
`
`Gil3
`
`II
`
`CH3CNH CCOCH3
`
`ii
`
`CH3
`
`jP /ZnCI2
`
`4r
`
`io
`CH3CNHdR
`
`CH3
`
`ROCH
`4Z ROH
`
`for 36 were in agreement with the values reported by
`Chadwick and Ngochindo and follow the pattern cited
`by Begtrup and co-workers for Nacetylimidazolel2a 40
`Our NMR decoupling experiments on 36 however
`quired reversal of the previously proposed C4 and C5
`The revised values mirrored the
`proton assignments
`NMR pattern reported for Nacetylimidazole2b 40
`The origin for
`the formation of
`the C4-imidazole-
`substituted derivative 37 has not been determined Pre-
`vious studies have shown that treatment of the C2-lithio
`salt of 36 with alkyl halides furnished the C2 substituted
`product while addition of electrophiles to the C2C5-
`dilithio intermediate provided the C5-substituted adduct
`as major product
`
`re-
`
`CH3NHC _NHCH2Q
`
`R1
`
`Br
`
`A2
`
`CN
`
`R2
`
`JJ_SO2NCH32
`
`A2 CONH2
`
`42 A2 CSNH2
`
`42 A2 CNOHNH2
`
`CHOCH2CH32
`
`R4
`
`SO2NCH32
`
`SO2NCH32
`
`CH3
`
`R4 CH
`
`cocH3 R4
`
`Comparable protocols were employed for the prepara-
`tion of the N-substituted heteroaromatics 1317 beginning
`with 33 Addition of an excess amount of the preformed
`potassium salt of pyrrole to 33 in tetrahydrofuran yielded
`13 while 1417 were synthesized by initial
`treatment of
`33with excesstriethylamine at78
`followed by addition
`of the parent heterocycle
`a-Acetamido-N-benzyl-a-cyanoacetamide 34 served as
`for the synthesis of 11 12 and 1820
`the starting point
`Addition of formic hydrazide to 34 in basic ethanol gave
`11 upon workup while treatment of 34 with KN3 and
`
`triethylamine hydrochloride in 1-methyl-2-pyrrolidinone
`afforded 12.13 a-Oxazol-2-yl 18 and a-thiazol-2-yl 19
`derivatives were prepared by initial conversion
`of 34 to
`the a-amide9 41 and a-thioamide 42 adducts respec
`tively and then these compounds were condensed with
`excess bromoacetaldehyde dimethyl acetal4 in diniethox
`yethane a-Oxadiazol-3-yl 20 derivative was generated
`in two steps from 3415 Addition of NH2OH.HC1 to 34 in
`basic ethanol gave the a-carboxamide oxime derivative
`43 Treatment of 43 with trimethyl orthoformate and
`catalytic amount of boron trifluoride etherate gave 20
`Several synthetic protocols were utilized for the prep
`132 Catalytic hydrogenation H2
`aration of compounds
`Pd/C of RS-4 gave the tetrahydrofuran-2-yl adduct 21
`recrystallization of the product mixture from
`Fractional
`ethyl acetate provided diastereomers 21a and 21b Syn
`thesis of the a-methyl analogue 22 was achieved by four
`step procedure Scheme
`beginning with methyl 2-ac-
`etainidoacrylate6 44 Addition of HBr to 44 furnished
`45 which was directly treated with furan and ZnC12 to
`adduct 46.617 Hydrolysis of
`give the a-amidoalkylation
`46 to the free acid 47 followed by treatment of 47 with
`benzylamine using the mixed carbonic anhydride coupling
`procedure68 i.e isobutyl chloroformate 4-methylmor-
`pholine gave 22
`The two thioamides 23 and 24 were prepared directly
`from using Lawessons reagent.9 Treatment of with
`this thiation reagent 0.5 molar equiv at room temperature
`yielded the monothio derivative 23 Elevation of the
`and the relative proportion
`reaction temperature
`of
`molar equiv to
`Lawessons reagent
`gave the dithio
`product 24
`Synthesis of 25 26 and 29 was accomplished from
`acid 48 isobu
`racemic cr-acetamido-a-furan-2-ylacetic
`tyl chloroformate 4-methylmorpholine and the appro
`priate amine or hydrazine while use of R-a-acetamido
`in this protocol with
`a-furan-2-ylacetic acid6
`and 4-trif-
`4-fluorobenzylamine
`4-methylbenzylamine
`luoromethylbenzylaniine furnished the three optically
`active N-benzylamides R-30R-32 respectively This
`coupling strategy previously provided enantiopure R-4
`and S4.6 Evidence
`that amide bond formation pro
`
`

`
`3354
`
`Journal of Medkinal Chemistry 1993 Vol 36 No 22
`
`ceeded without
`
`racemization 5% was obtained by
`NMR spectra CDC13 of RS-30 and
`examining the
`R-30R-32 both in the absence and the presence of
`saturating amounts of R--mandelic acid.2 Addition
`to RS-30 led to the
`of
`this chiral solvating reagent
`appearance of two acetyl methyl signals -s ppm 0.02
`of equal intensity2 while only single acetyl methyl singlet
`NMR spectra for
`was observed in the corresponding
`R-30R-32 Similar results were earlier secured for R-
`S-4 and RS-46 see the supplementary material for
`NMR spectra
`Access to the starting
`appropriate
`material R-48 was readily achieved using the protocol
`advanced by Whitesides and co-workers.22 Treatment of
`racemic 48 with acylase
`led to the selective hydrolysis
`of the S-amino acid derivative providing R-48 in 757
`yield Previously R-48 was obtained by fractional
`
`CH3CNH
`
`II
`
`COH
`
`recrystallization of the corresponding diastereomeric salts
`formed with R-a-methylbenzylamine.6The two pyridine
`N-oxide adducts 27 and 28 were prepared by treating 25
`and 26 respectively with m-chloroperoxybenzoic acid
`
`Pharmacological Evaluation
`The heteroaromatic amino acid derivatives 932 were
`tested for anticonvulsant activity using the procedures
`described by Krall and co-workers23 and these results were
`compared to the findings previously reported for 3_8.6 All
`compounds were administered intraperitoneally ip to
`mice Tables
`and II
`the ED50 values required to
`list
`toxic extension of the hind limbs in mice in the
`prevent
`MES test by 932 Included in these tables are the median
`neurologically impairing dose TDso values using either
`the horizontal screen24 HS or the rotorod test.25
`In most
`cases the TD50s were only determined for those corn-
`pounds that had good activity in the MES test The
`protective index PT
`TD50/ED50 for these adducts where
`appropriate is also shown in Tables
`and II
`Our previous studies indicated that placement of
`electron-rich five- and six-membered aromatic and het-
`
`eroaromatic moieties at the a-site within functionalized
`amino acids
`led to compounds providing excellent
`protection against MES-induced seizures in mice.6 More-
`over we noted in this series that improved activity resulted
`heteroatom two atoms removed
`by the positioning of
`from the Ca-site
`similar result was observed
`in
`The pharmacological data
`a-acyclic derivatives of
`obtained in this study provided evidence
`in support of
`these two structureactivity themes
`Support for the beneficial value accrued by the place-
`ment of an electron-rich aromatic ring at the Ca-position
`was obtained by the comparison of the ED50 values in the
`ED50
`16.1 mg/kg versus the
`MES-test
`for pyrrole
`azoles 912 ED50
`The data
`30 mg/kg Table
`demonstrated that overall
`reduction of
`the electron
`of the Ca ir-aromatic system by
`excessive character
`heteroatom incorporation26 led to decreased biological
`activity despite the fact that additional nitrogen incor-
`substrate that contained two
`poration often provided
`heteroatoms two atoms removed from the Ca-site i.e
`11 12
`
`Kohn et al
`
`Comparison of
`the pharmacological activities of the
`912 versus the N-substituted
`C-substituted azoles
`isomers 1317 provided qualitative information concerning
`the importance of heteroatom substitution versus the Ca
`position We observed
`significant reduction in activity
`16.1 mg/kg
`ED50
`for 13 ED50
`80.2 mg/kg versus
`and 17 ED50 300 mg/kg versus 12 ED50 30 100
`mg/kg In compound
`one heteroatom exists two atoms
`removed from the Ca-site while in 13 there is none
`Similarly in 12 there are two heteroatoms two atoms
`removed from the Ca-site while in 17 there is only one
`The delicate interplay of their-electron character of the
`appended Ca-heteroaromatic group the site of
`the
`heteroatom incorporation and the identity of the het
`eroatom on anticonvulsant
`activity was reinforced by
`comparison of the biological activities of the a-oxazol-2-yl
`18 a-imidazol-2-yl
`and a-thiazol-2-yl 19 derivatives
`Of these three compounds 18 was the most active ED50
`10.4 mg/kg
`displaying protection similar to that
`9.5 mg/kg.8 The slight
`reported for phenytoin ED50
`decrease in protection in the MES test afforded by 19
`ED50
`12.1 mg/kg
`versus
`18 paralleled the larger
`ED50
`difference previously observed for a-furan-2-yl
`10.3 mg/kg and a-thien-2-yl
`ED50
`44.8 mg/kg
`adducts.6 Surprisingly the a-imidazol-2-yl
`derivative
`the mice from MES-induced seizures at
`failed to protect
`dosages of 100 mg/kg or less Previously we observed
`that
`the anticonvulsant activity of
`decreased in pro-
`ceeding from oxygen to nitrogen to sulfur containing Ca
`heteroaromatic derivatives.8 The low potency of may be
`the increased
`reflection in part of
`basicity of
`compound versus 18 and 19
`The pyrazole derivative 14 provided protection in the
`MES test ED50
`16.5 mg/kg comparable to phenobar
`bital ED50
`21.8 mg/kg8 and this compound was
`considerably more potent than the isomeric imidazoles
`10 and 15 Our
`results do not provide information
`the underlying factors that contribute to this
`concerning
`difference in activity We do note that pyrazoles are
`substantially less basic than imidazoles.26
`Inspection of the composite data set for analogues of
`re
`a-acetamido-N-benzyl-a-furan-2-ylacetamide
`vealed that most structural changes at the a-carbon amide
`carbonyl and N-benzylamide site in
`led to decreased
`as anticonvulsants Table II
`potency of the compounds
`is in agreement with previous findings dem
`This result
`onstrating that stringent steric and electronic factors
`governed
`the anticonvulsant
`activities of
`this class of
`compounds.3467 Examination of the individual
`test results
`important observations First reduction of
`led to several
`to the tetrahydrofuran analogues 21a
`the furan ring in
`and 21b led to
`decrease but not an abolition of activity
`in the MES test i.e ED50
`90 mg/kg The decreased
`can be attributed to the loss of the
`activity of 21 versus
`aromatic ring at the a-carbon site since previous findings
`have demonstrated that substantial
`improvement
`in
`the placement of
`activity accompanied
`small aromatic
`group at this position.6 The potency of 21a and 21b was
`greater than that observed for 49 ED50 100 mg/kg.9b
`This observation provided support for our suggestion that
`increased anticonvulsant activity generally accompanied
`the placement of substituted alkylated heteroatom two
`atoms removed from the amino acid a-carbon.7 Second
`replacement of the a-carbon proton in by methylgroup
`led to
`sharp decrease in anticonvulsant activity of the
`drug candidate This decreased potency in the MES test
`
`this
`
`

`
`a-Acetamido-N-benzylacetamide
`
`Derivatives
`
`Journal of Medicinal Chemistry 1993 Vol 36 No 22
`
`3355
`
`R2
`
`CH3CNH CNHCH2_Q
`
`A2
`
`CH2OH
`CH3
`
`CH3
`
`CH3CNHCCNHCH2-4J
`CH3
`
`1330 and 283 spectrometers and were calibrated against the
`1601-cnr band of polystyrene Absorption values are expressed
`NMR and carbon 3C NMR
`in wavenumbers cnr Proton
`nuclear magnetic resonance spectra were taken on Nicolet NT
`300 and General Electric QE-300 NMR instruments Chemical
`are in parts per million ppm relative to Me4Si and
`shifts
`values are in hertz Low-resolution mass
`coupling constants
`spectra MS were recorded at an ionizing voltage of 70 eV with
`Varian MAT CH-5 spectrometer at the Lilly Research Lab-
`oratories High-resolution
`electron-impact mass spectra were
`performed on aVG ZAB-E instrument by Dr
`Moini at the
`University of TexasAustin Microanalyses were provided by
`the Lilly Research
`the Physical Chemistry Department
`of
`and Lawessons
`Laboratories
`Ethyl acetamidocyanoacetate
`
`10cm
`
`5.51
`
`7.30
`
`was surprising in light of the near equipotency previously
`51.0 mg/kg5 versus 51 ED50
`observed for 50 ED50
`40
`100 mg/kg.27 Third isosteric replacement of the
`amide carbonyl groups in by thioamide moiety resulted
`in decreased potency in the MES test Of the two amide
`groups modification of the benzylamide moiety i.e 24
`appeared to affect the MES activity more than modifi-
`cation of the acetamide site i.e 23 Fourth alteration
`of the N-benzylamide group affected the pharmacological
`profile of the functionalized amino acid test candidate
`Conversion of the N-benzylaniide substituent
`to the
`in
`3-pyridinylmethyl 25 or the corresponding N-oxide 27
`led to small decreases in anticonvulsant activity whereas
`the isomeric 4-pyridinylmethyl adduct 26 and N-oxide
`28 were devoid of anticonvulsant activity at doses less
`than 100 mg/kg Similarlythe 2-pyridine hydrazide 29
`displayed no protective effects in the MES test at doses
`less Fifth the pharmacological
`of 100 mg/kg or
`reospecificity that distinguishes this novel class of anti-
`convulsant agents was reaffirmed by the biological data
`obtained for R-30 R-31 and R-32 We noted
`in anticonvulsant activity of R-
`improvement
`significant
`3.5 mg/kg versus the corresponding racemate
`30 ED50
`the potency of R-30
`12.7 mg/kg Moreover
`306 ED50
`exceeded the value previously reported for phenytoin ED50
`9.5 mg/kg.8
`
`ste-
`
`Conclusions
`
`Synthetic protocols have been developed
`for the gen-
`eration of Ca-heteroaromatic a-acetamido-N-benzylac-
`etamides The pharmacological activities of these unique
`amino acid derivatives i.e 920 along with the modified
`analogues of a-acetamido-N-benzyl-a-furan-2-ylacet-
`amide i.e 2132 extended the structureactivity rela-
`tionships previously obtained for this class of anticon-
`Significantly the a-furan-2-yl
`vulsant agents.7
`a-oxazol-2-yl 18 and a-thiazol-2-yl 19 a-acetamido-
`N-benzylacetamides afforded excellent protection to MES-
`induced seizures in mice The observed ED50 and P1 values
`rivaled those reported for phenytoin.5 The experimental
`findings provided further documentation of the beneficial
`properties gained by the incorporation of aromatic groups
`at the Cci-site and the importance of heteroatom location
`within the aromatic ring system for maximal biological
`activity Protection against MES-induced seizures proved
`and to
`to be sensitive to changes at the Ca-site in
`modifications conducted ateachofthe other keyfunctional
`groups in these compounds
`
`Experimental Section
`chemistry General Methods Melting points were deter-
`mined with Thomas-Hoover melting point apparatus and are
`Infrared spectra ER were run on Perkin-Elmer
`uncorrected
`
`reagent
`24-disulfide were obtained from Aldrich Chemical Co Mil
`waukee WI Thin-layer chromatography was performed on
`precoated silica gel GHLF microscope slides 2.5
`No 21521
`Synthesis of a-Acetamido-N-benzyl-a-imldazol-2-yl-
`in hexane 6.8 mL 17.0 mmol
`acetamide
`n-BuLi 2.5
`cooled 46
`solution of 350 2.90
`was added to
`17.06
`mmol in THF 45 mL under N2 and then stirred at -46
`15
`mm The lithio salt solution of 35 was then added dropwise 15
`mm into cooled 78
`THF solution l3OmL of 33 prepared
`from a-acetamido-N-benzyl-a-ethoxyacetamide7
`2.00
`in CH2C12 10 mL 10.0 mmol.7 The
`mmol and BBr3
`reaction was stirred at 78
`and then quenched with
`saturated aqueous NH4C1 50 mL solution The mixture was
`stirred at room temperature 30 mm and made basic pH 9.2
`with aqueous K2C03 The aqueous mixture was extracted with
`100 mL and the combined extracts were dried Nas
`EtOAc
`SO4 The solvents were removed in vacuo and the residue was
`on Si02 gel 2.5%
`purified by flash column chromatography
`7% of
`MeOH/CHC13
`mp 228230
`to give 0.14
`recrystallized from EtOH
`0.46 10% MeOH/CHC13
`KBr 3200 br 1610 1500 br 1430 1350 740 680 cm-
`COCH3 4.29
`NMR DMSO-d6 81.91
`5.6 Hz CH2
`7.7 Hz CH 6.85 hr sC4H 7.05 br sC5H 7.18
`7.7 Hz NH 8.65
`PhH 8.42
`5.6 Hz
`NH 11.91 hr NE 3C NMR DMSO-d8 22.49 COCH3
`42.21 CH2 51.62 CH 126.60 C4 126.98 2C5or 2C3 127.21
`Cg 128.09 2C2 or 2C3 128.32 C5 139.05 Ci 143.74 C2
`168.12 CONH 169.30 COCH3 ppm mass spectrum FD
`65 272
`100 Anal
`relative intensity 273
`C14H6N402
`Synthesis of a-Acetamido-N-benzyl-a-imidazol-4-yl-
`acetamlde 10
`75% aqueous EtOH 16 mL solution of 37
`3.05 mmol was acidified pH 1.5 with ethanolic HC1
`0.85
`The reaction was
`and the solution was heated to reflux
`neutralized with saturated aqueous NaHCO3 solution and the
`EtOHH2O a.zeotrope removed by distillation
`in vacuo The
`remaining aqueous layer was made basic pH 10 with aqueous
`NaOH The aqueous mixture was extracted with EtOAc
`50
`rnL and the combined extracts were dried Na2SO4 The
`reaction mixture was concentrated in vacuo to give 0.35 57%
`of 10 rnp 189191
`dec recrystallized from acetone R1 0.19
`IR KBr 3400 3260 1650 1600 1500
`10% MeOH/CHC13
`NMR DMSO-d6
`1430 1360 1330 730 710 cm-
`6.8 Hz CH
`COCH3 4.28
`5.9 Hz CH2 5.38
`PhH 7.60 C2H 8.26 br
`6.97 hr C5H 7.157.30
`NH 8.53 br sNH 12.01 hr NH
`NMR CD8OD 22.45
`COCH3 44.15 CH2 127.88 C5 or C4 128.01 C4 or C5
`128.37 2Cr or 2Cr 129.44 2Cr or 2Cr 136.88 C2 139.74
`172.13 CONH 173.00 COCH3 ppm
`weak signal
`was observed at 654 and has been tentatively attributed to CH
`mass spectrum FD 273
`Anal C4H16N402
`Synthesis of a-Acetarnldo-N-benzyl-a-124-trlazol-3-yl-
`acetamide 11 An ethanolic solution 250 mL of 349 3.00
`13.0 mmol formic hydrazide 1.60
`26.0 mmol and K2C03
`2.90 mmol was heated at reflux 20
`The reaction
`6.00
`mixture was allowed to cool and filtered and the solvent was
`removed in vacuo The residue was purified by flash column
`on Si02 gel using 13% MeOH/CHC13
`as the
`chromatography
`eluant to give 1.40 40% of the desired product Compound
`11 was purified by recrystallization from EtOH mp 205207
`IR KBr 3285 3080 2930 1690
`R1 0.35 16% MeOH/CHC13
`
`8.0
`
`IR
`
`1.88
`
`

`
`3356
`
`Journal of Medicinal Chemistry 1993 Vol 36 No 22
`
`Kohn et al
`
`1.92 COCH1 4.30
`NMR DMSO-d6
`1650 1510 cm-1
`7.8 Hz CE 7.187.32
`5.7 Hz CH5 5.62
`7.8 Hz NH 8.71
`C5H 8.56
`Phil 8.53
`Hz NH 13.98 NH
`NMR DMSO-d5 22.48 COCH3
`42.41 CH 51.30 CH 126.63 C4 127.08 2C2 or 2C5 128.11
`167.92 CONH 169.32 COCH3
`2C2 or 2C3 139.05
`ppm the two triazole carbon signals were not detected mass
`100 273 66
`spectrum FD relative intensity 274
`Anal C13H15N502
`Synthesis of a-Acetamido-N-benzyl-a-tetrazol-5-yl-
`acetamide 12 mixture of 34 1.00
`4.33 mmol KN3 1.70
`20.96 mmol and Et3N.HC1 1.78
`13.0 mmol in 1-methyl-
`125 mL was stirred at 110
`After
`2-pyrrolidinone
`cooling aqueous concentrated HC1 mL was added and the
`reaction mixture was filtered The solvent was removed in uacuo
`NaOH 20 mL and
`The residue was dissolved in aqueous
`HC1 20 mL was added The precipitate was
`then aqueous
`filtered to give 0.77 65% of the desired product Compound
`R0.20 30%
`12 was recrystallized from EtOH mp 236238
`MeOH/CHC18 IR KBr 330032603080168016451500cm-
`1.94 COCH5 4.33
`NMR DMSO-d6
`5.7 Hz
`7.8 Hz CE 7.187.33
`CH2 5.89
`Phil 8.86
`7.8 Hz NH 8.92
`5.7 Hz NH 16.54 br sNH SC
`NMR DMSO-d6 22.21 COCH3 42.37 CH2 48.13 CH
`126.67 C4 127.00 2C2 or 2C3 128.05 2C2 or 2C5 138.52
`C1 166.18 CONH 169.58 COCH ppm the tetrazole
`carbon signal was not detected mass spectrum FD relative
`173 274 100 CI 274.119201 calcd
`intensity 275
`for C2H4N5O2 274.117824
`Synthesis of a-Acetamido-N-benzyl-a-l-pyrrolylacet-
`amide 13
`cooled 78
`THF solution 225 mL of 33
`prepared from a.acetamido-N-benzyl-a-ethoxyacetamide
`2.00
`CHC12 solution 8.8 mL 8.8 mmol
`8.0 mmol and BBr3
`was added under N2 to cooled 78 CC suspension of potassium
`25.8 mmolinTHF 25 mL The reaction mixture
`pyrrole 2.71
`was stirred at 78
`and then at room temperature
`and then treated with H20 10 mL and acidified pH 4.0 with
`5% citric acid
`The reaction was made basic with aqueous
`saturated Na2CO3 solution the aqueous mixture was extracted
`250 mL and the combined organic layers were
`with EtOAc
`dried Na2SO4 The volatile materials were removed in vacuo
`and the residue was purified by flash column chromatography
`on Si02 gel using 3% MeOH/CHC18
`as the eluant to give 0.40
`18% of the desired product Compound 13 was purified by re-
`R0.44 4% MeOH/
`crystallization from EtOH mp 182184
`CHC13 IR KBr 34003280 1630 1520 1370 740720cm-
`1.91 COCH3 4.30
`NMR DMSO-d6
`5.5 Hz CE2
`8.7 Hz CH 6.85
`C2H
`C3H 6.38
`6.01
`5.5 Hz NH 9.14
`7.11-7.35 in Phil 8.96
`Hz NH 3C NMR DMSO-d6 22.22 COCH 42.15 CH2
`62.86 CH 107.79 2C5 119.19 2C2 126.76 Cg 127.01 2Cr
`or2C3 128.11 2Cyor2Cr 138.34 C1 166.37 CONH 189.41
`COCH3 ppm mass spectrum FD relative intensty 272
`22 271
`100 Anal C5H7N302.0.2H20
`Synthesis of a-Acetamido-N-benzyl-a- 1-pyrazolyl-
`acetamide 14 To
`cooled 78
`solution 250 mL of 33
`prepared from a-acetaxnido-N-benzyl-a-ethoxyacetamide
`3.60
`CH2C12 solution 15.8 mL 15.8
`14.4 mmol and BBr3
`28.8 mmol in THF 20 mL
`mmol was added EtN 2.91
`17.28 mmol in THF 30 mL The
`followed by pyrazole 1.17
`mixture was stirred at 780C 30 mm and at room temperature
`The insoluble materials were filtered and the solvents
`removed in vacuo The residue was purified by flash column
`chromatographyonSiO2gelusing4% MeOH/CHCl3astheeluant
`to give 0.80 22% of the desired product Compound 14 was
`recrystallized from EtOAc as white solid mp 158160 CC R1
`0.51 6% MeOH/CHCI
`IR KBr 34003180 1650 1530 1470
`1370 1350 740 700 cm NMR DMSO-d6
`1.93 CO-
`5.8 Hz CE2 6.26
`CH3 4.29
`C4H 6.57
`Hz CE 7.15-7.33
`Phil 7.48 br sC5H 7.76 bra C3H
`5.8 Hz NE 9.23
`8.8 Hz NH 3C NMR
`DMSO-d6 22.41 COCH3 42.40 CM2 65.51 CH 105.37
`C4 126.87 C4 127.14 2Cr or 2Cr 128.25 2C3or 2C3 129.00
`C5 138.59 Cs 139.17 Cj 165.68 CONH 169.81 CO-
`CH3 ppm mass spectrum FD relative intensity 273
`13983 138 100 92 37 Anal C4H6N402
`11 272
`
`5.7
`
`8.7
`
`8.8
`
`8.96
`
`Synthesis of a-Acetamido-N-benzyl-a-1-lmldazolyl-
`acetainide 15 Using the preceding procedure a-acetaniido
`8.0 mmol B8r3
`CH2-
`N-benzyl-a-ethoxyacetaniide
`2.00
`Cl2 solution 8.8 mL 8.8 mmol Et3N 1.62
`1.60 mmol and
`8.8 mmol gave 0.60 80% of 15 The desired
`imidazole 0.60
`compoundwasrecrystallizedfromethylacetate/hexaneasabeige
`0.30 7% MeOH/CHC13
`colored solid mp 146148
`IR
`KBr 3400 br 1640 1560 1480 1360 720 670 cm-1
`NMR
`DMSO-d6 1.85 COCH3 4.30 br CE2 6.53
`Hz CE 6.89 C5H 7.127.33 in C4B Phil 7.69 C2R
`9.06 br NH 9.29
`8.0 Hz NE 8C NMR DMSO-d6
`22.28 COCH3 4