合成路线1

The reaction of (S)(-)-lactic acid methyl ester (I) with Ts-Cl and TEA in dichloromethane gives the corresponding tosylate (II), which is condensed with 4-(benzyloxy)phenol (III) by means of NaH in DMF to yield (R)(+)-2-[4-(benzyloxy)phenoxy]propionic acid methyl ester (IV). The hydrogenolysis of the benzyl group of (IV) with H2 over Pd/C in ethyl acetate affords the 4-hydroxyphenoxy compound (V), which is condensed with 2,7-dichloroquinoxaline (VI) by means of K2CO3 in refluxing acetone, provides the ester precursor (VII). The hydrolysis of (VII) with KOH in THF/water, followed by acidification with HCl, gives the chiral propionic acid (VIII), which is finally converted into its sodium salt with NaOH in water.

合成路线2

The bromosulfonate (XXI) has been obtained as follows: (S)-Lactic acid methyl ester (XXII) has been protected as its benzyloxymethyl ether (XXIII) according to Tetrahedron Lett 1980, 21: 1035. The reduction of (XXIII) with DIBAL yields the corresponding aldehyde (XXIV), which by a Grignard reaction with ethylmagnesium bromide in THF and chromatographic separation of the diastereoisomers (SiO2, hexane/ethyl acetate) affords 2(S)-(benzyloxymethoxy)-3(R)-pentanol (XXV). Finally, this compound is sulfonated to (XXI) with 4-bromobenzenesulfonyl chloride. Finally, compound (XX) is condensed with 2(S)-(benzyloxymethoxy)-3(R)-pentanol 4-bromobenzenesulfonate ester (XXI) by means of cesium carbonate in DMF, and deprotected with 6N HCl.

合成路线3

Methyl (S)-lactate (I) was converted to chloride (II) by treatment with SOCl2. Subsequent displacement in (II) by cesium thioacetate produced thioester (III). Reduction of the ester group of (III) with concomitant thioester cleavage by means of LiAlH4 in cold THF furnished mercaptoalcohol (IV).

合成路线4

Methyl (S)-lactate (XXVI) was protected as the benzyloxymethyl ether (XXVII) and subsequently reduced to aldehyde (XXVIII) with DIBAL in toluene at -78 C. Addition of ethylmagnesium bromide to this aldehyde (XXVIII) produced a diastereomeric mixture of carbinols. The required (2S,3R) isomer (XXIX) was isolated by column chromatography and then converted to brosylate ester (XXX) by reaction with 4-bromobenzenesulfonyl chloride. Nucleophilic displacement of the brosylate group of (XXX) by triazolone (XXV) produced the N-alkylated triazolone (XXXI). Then, acid cleavage of the benzyloxymethyl protec-ting group of (XXXI) provided alcohol (XXXII).

合成路线5

In an alternative synthesis of compound (XXXII), methyl (S)-lactate (XXXIII) was converted to amide (XXXIV) by treatment with pyrrolidine, and then protected as the benzyl ether (XXXV). Reduction of (XXXV) by means of sodium bis(methoxyethoxy)aluminum hydride produced aldehyde (XXXVI). Condensation of (XXXVI) with formic hydrazide produced the formyl hydrazone (XXXVII), to which was added ethylmagnesium bromide affording a mixture of diastereoisomeric hydrazides. Separation by column chromatography provided the required (S,S) isomer (XXXVIII). Cyclization of (XXXVIII) with the phenyl carbamate (XXIII) in the presence of DBU furnished the triazolone (XXXIX). This was deprotected by hydrogenation in the presence of Pd/C and formic acid to produce compound (XXXII)

合成路线6

Synthesis of intermediates (XX) and (XXIII): Coupling of methyl L-lactate (XII) with morpholine in presence of NaH yields amide (XIII) which is tosylated by means of NaH and p-TsCl in THF to afford (XIV). Reduction of carboxylic acid (XV) in DCE with B(OCH3)3, boron trifluoride diethyl etherate and BH3·pyr complex provides alcohol (XVI) which is then condensed with (XIV) in presence of K2CO3 in DMF to yield (XVII). Mesylation of (XVII) with MsCl in presence of Et3N in CH2Cl2 affords (XVIII), which reacts with potassium phthalimide (C) in DMF to give (XIX). Hydrogenation of phthalimide (XIX) with H2 over Pd/C in DMF provides derivative (XX). The treatment of (XIX) with NH2NH2 and p-TsOH gives amine (XXI), which is protected with di-t-butyl-dicarbonate to yield (XXII). Finally (XXIII) is obtained by reduction of the nitro moiety of (XXII) with H2 over Pd/C in EtOAc.

合成路线7

The reaction of (S)-(+)-methyl lactate (I) with pyrrolidine (II) gives the corresponding acyl pyrrolidine (III), which is silylated with Tbdms-Cl and imidazole to yield the silyl ether (IV). The condensation of (IV) with 3,4-difluorobromobenzene (V) by means of BuLi in THF affords the chiral propiophenone derivative (VI), which is treated with hydroxylamine and NaOAc in methanol to provide the corresponding oxime (VII). The reduction of (VII) with LiAlH4 in refluxing ethyl ether gives the expected amine (VIII), which is treated with (Boc)2O in chloroform, yielding the carbamate (IX). The cyclization of (IX) by means of NaH in THF gives a mixture of cis- and trans-oxazolidinones, from which the desired trans-(4S,5S)-isomer (X) is separated by flash chromatography. The reaction of (X) with 4-nitrophenyl chloroformate (XI) by means of NaH yields the oxazolidinone-carboxylate (XII), which is finally condensed with 3-[4-(4-fluorophenyl)piperidin-1-yl]propylamine (XIII) in THF to afford the target amide.

合成路线8