合成路线1

In an alternative procedure, condensation of L-valine (IV) with methyl acetoacetate (V) in the presence of NaOH produced the enamine-protected valine sodium salt (VI). Condensation of (VI) with the tosylate (VII), (prepared from acyclovir (I) and tosyl chloride) afforded ester (VIII). Then, acidic hydrolysis of the enaminoester moiety of (VIII) furnished the target valine ester. Similar procedures were also reported using omega-mesyl and omega-chloro acyclovir.

合成路线2

Diazotization of (S)-valine (LXXXIX) gave rise to the alpha-hydroxyacid (XC), which was reduced to diol (XCI) using LiAlH4. Tosylation of the primary hydroxyl of (XCI), followed by cyclization of the resulting tosylate (XCII) under basic conditions, furnished epoxide (XCIII). Condensation of epoxide (XCIII) with the lithium anion derived from sulfone (LXXXVIII) gave adduct (XCIV). Reductive elimination of the phenylsulfonyl group and then acidic rearrangement of the cyclopropane ring provided the dihydroxy steroid (XCV). After protection of (XCV) as the diacetate (XCVI), allylic oxidation with CrO3 in the presence of dimethylpyrazole yielded enone (XCVII).

合成路线3

The condendsation of epoxide (V) with (2S,4R)(VI) by means of basic alumina in THF, followed by elimination of the protecting group with HCl and NaOH yields directly the condensation product (XVIII) as a pure diastereomer and with a free amino group. Finally, this compound is condensed with N-(2-quinolylcarbonyl)-L-valine (XIX) through its activation compound with isobutyl chloroformate (the 4(S)-isopropyl-2-(2-quinolyl)oxazol-5(4H)-one (XX)). The N-acyl-L-valine (XIX) has been obtained by acylation of L-valine (XXI) with quinoline-2-carboxylic acid (X) through its acyl chloride obtained with SOCl2.

合成路线4

The condensation of L-valine (I) with 4-fluorobenzenesulfonyl chloride (II) by means of NaOH in THF/water gives N-(4-fluorobenzenesulfonyl)-L-valine (III), which is esterified with N-hydroxysuccinimide (IV) by means of EDC in dichloromethane to yield the activated ester (V). The condensation of (V) with L-leucinol (VI) by means of TEA in dichloromethane affords the N-(4-fluorobenzenesulfonyl)-L-valyl-L-leucinol (VII), which is finally oxidized with the SO3/Pyridine complex in DMSO/dichloromethane to provide the target leucinal derivative.

合成路线5

(S)-2-Hydroxyisovaleric acid (IX) was obtained from L-valine (VIII) by diazotization in the presence of sulfuric acid. After protection as the allyl ester (X), coupling with isostatine derivative (VII) using DCC and DMAP afforded (XI). Then, removal of the allyl group of (XI) by means of Pd(PPh3)4 gave acid (XIII), which was activated as the pentafluorophenyl ester (XIII).

合成路线6

The synthesis of the carboxylic acid intermediate (VIII) has been performed as follows: The reaction of D-valine (I) with benzyl chloroformate and NaHCO3 gives the protected valine (II), which is esterified with pentafluorophenol and EDAC to yield the activated ester (III). The condensation of (III) with the lithium enolate of methyl acetate (IV) affords the beta ketoester (V), which is stereoselectively reduced with KBH4 and crystallized to afford the desired enantiomeric beta hydroxyester (VI). The silylation of (VI) with Tips-OTf and lutidine provides the silyl ether (VII), which is hydrolyzed with NaOH to give the desired carboxylic acid intermediate (VIII). The synthesis of the activated ester intermediate (XV) has been performed as follows: The reaction of L-valine (IX) with NaNO2 and H2SO4 gives the hydroxyacid (X), which is esterified with allyl bromide (XI) and K2CO3 to yield the allyl ester (XII). The condensation of (XII) with the intermediate (VIII) by means of EDAC and DMAP affords the adduct (XIII), which is treated with Pd(PPh3)4 to provide the carboxylic acid (XIV). Finally, this compound is esterified with C6F5-OTf to give the activated ester intermediate (XV).

合成路线7

Acylation of Evans oxazolidinone (II) with heptanoyl chloride (I) provides the chiral adduct (III). The lithium enolate of (III) is then diastereoselectively alkylated with tert-butyl bromoacetate (IV) to afford the succinate derivative (V). Removal of the chiral auxiliary group of (V) with lithium peroxide furnishes the carboxylic acid (VI), which is further activated as the succinimidyl ester (VII) upon treatment with N-hydroxysuccinimide and DCC. The activated ester (VII) is then condensed with L-valine (VIII), producing amide (IX). Subsequent coupling of (IX) with N-aminoproline methyl ester (X) leads to hydrazide (XI). After acidic tert-butyl ester cleavage in (XI), the resultant carboxylic acid (XII) is condensed with hydroxylamine to yield the desired hydroxamic acid.

合成路线8