3) The alkylation of 5(S)-(tert-butyldimethylsilyloxymethyl)tetrahydrofuran-2-one (XII) by means of benzyl bromide (XIII) and lithium diisopropylamide (LDA) gives the corresponding 3(R)-benzyl derivative (XIV), which is deprotected with aqueous HF, yielding the hydroxymethyl compound (XV). The esterification of (XV) with trifluoromethanesulfonic anhydride affords the corresponding triflate (XVI), which is condensed with the chiral piperazine (VII) by means of diisopropylethylamine in isopropanol, giving the substituted furanone (XVII). Ring opening of the furanone (XVII) with LiOH, DME and imidazole yields the substituted hydroxypentanamide (XVIII), which is protected with tert-butyldimethylsilyl chloride to afford the protected amide (XIX). The trans-amidation of (XIX) with 2-hydroxyindan-1-amine (II) by means of 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide (EDC) and 1-hydroxybenzotriazole (HOBt) in DMF gives the protected dihydroxy diamide (XX), which is deprotected with trimethylsilyl triflate, affording the dihydroxy diamide (VII), already obtained. This compound is then alkylated with 3-(chloromethyl)pyridine (IX) as before.
5) The double bond of the pentenylamide (X) (as obtained in Scheme 1) is oxidized with OsO4 and N-methylmorpholine N-oxide in tert-butanol/water to give the 4(R,S),5-dihydroxy-compound (XXVI), which is esterified selectively with methanesulfonyl chloride, yielding the terminal monomesylate (XXVII). The condensation of (XXVII) with the chiral piperazine (VII) by means of K2CO3 in hot isopropanol yields the condensation product (XXVIII) with the (R,S)-configuration at the 4-OH group. The optical resolution of this 4-OH group with (S)-(+)-camphosulfonic acid affords the protected hydroxy-amide (XXV), already obtained in Scheme 19918303a.
6) The chiral piperazine (VII) can be obtained by several different ways: 6a) The sequential protection of piperazine-2(S)-carboxylic acid (XXIX) gives 1-(benzyloxycarbonyl)-4-(tert-butoxycarbonyl)piperazine-2(S)-carboxylic acid (XXX), which is condensed with tert-butylamine by means of EDC and HOBt to afford the tert-butylamide (XXXI). Finally, this compound is selectively deprotected by hydrogenation with H2 over Pd/C in methanol, yielding the chiral piperazine (VII). 6b) The partial hydrogenation of N-tert-butylpyrazine-2-carboxamide (XXXII) with H2 over Pd/C gives the tetrahydro derivative (XXXIII), which is sequentially protected as usual to the 1-(benzyloxycarbonyl)-4-(tert-butoxycarbonyl)-1,4,5,6-tetrahydropyrazin e -2-carboxamide (XXXIV). Finally, this compound is hydrogenated using the chiral catalyst [R-BINAP(COD)Rh]OTf to afford the chiral piperazine (XXXI), already obtained. 6c) The N-tert-butylpyrazine-2-carboxamide (XXXII) is fully reduced with H2 over Pd/C in propanol, giving the racemic N-tert-butylpiperazine-2-carboxamide (XXXV), which is submitted to optical resolution with (S)-(+)-camphosulfonic acid, yielding the (S)-isomer (XXXVI), which is then selectively protected with tert-butoxycarbonyl anhydride to give the desired chiral amide (VII).
1) The reaction of cis-(1S,2R)-indanediol (I) with acetonitrile and concentrated H2SO4 gives cis-(1S,2R)-1-aminoindan-2-ol (II), which is cyclocondensed with 3-phenylpropionyl chloride (III), isopropenyl methyl ether and triethylamine to yield the acetonide amide (IV). The condensation of amide (IV) with (S)-(+)-glycidyl p-toluenesulfonate (V) in the presence of lithium hexamethyldisylazide (LHS) affords the chiral epoxide (VI), which is condensed with 4-(tert-butoxycarbonyl)-N-tert-butylpiperazine-2(S)-carboxamide (VII) in refluxing isopropyl acetate and deprotected with aqueous HCl to give the dihydroxy-diamide (VIII). Finally, this compound is condensed with 3-(chloromethyl)pyridine (IX) by means of triethylamine in DMF. 2) The amide (IV) can also be alkylated with allyl bromide and butyllithium to the pentenyl amide (X), which is diastereoselectively converted to the chiral iodohydrine (XI) by means of N-iodosuccinimide (NIS). Finally, this compound is cyclized in basic medium, yielding the epoxide (VI), already obtained.
4) The condensation of the chiral piperazine (VII) with (S)-(+)-glycicyl 3-nitrobenzenesulfonate (XXII) by means of diisopropylethylamine in DMF [or with (S)-glycidol (XXIII), tosyl chloride and NaH] gives the epoxide (XXIV), which is condensed with the propionamide (IV) by means of butyllithium in THF, yielding the protected hydroxyamide (XXV). The deprotection of (XXV) with aqueous HCl affords the dihydroxy-diamide (VIII), already obtained, which is finally alkylated with 3-(chloromethyl)pyridine (IX) as before.
The condensation of indeno[1,2-d]oxazole derivative (I) with (S)-(+)-glycidyl tosylate (II) by means of LiHMDS gives the adduct (III), which is deprotected with HCl to yield the epoxide (IV). Finally, this compound is condensed with the dibenzylpyrrolidone (V) by means of P4 phosphazene base (commercially available) in THF to afford the target amide.