合成路线1

Alkylation of 3-hydroxy-4-methoxybenzyl alcohol (I) with 1-bromo-3-methoxypropane (II) gives ether (III). Subsequent conversion of benzyl alcohol (III) into bromide (IV) is carried out using bromotrimetylsilane. The chiral isovaleryloxazolidinone (V) is alkylated with bromide (IV) by means of LiHMDS to afford (VI), which is hydrolyzed to the (S)-2-aryl-2-isopropylpropionic acid (VII) by means of lithium peroxide. The reduction of acid (VII) to the corresponding alcohol with NaBH4/I2 reagent, followed by treatment with PPh3 and NBS, provides bromide (VIII). Alkylation of the chiral dimethoxydihydropyrazin (IX) with bromide (VIII) produces (X). Further hydrolysis of the pyrazine ring of (X) with HCl, followed by Boc protection of the resulting (S,S)-amino ester, yields compound (XI). Reduction of the ester group of (XI) with DIBAL gives aldehyde (XII). This compound is condensed with the Grignard reagent (XIII) to afford the diastereomeric mixture of amino alcohols (XIV). Treatment of mixture (XIV) with 2,2-dimethoxypropane (XV) and TsOH produces a mixture of oxazolidines, from which the required (S,S,S)-isomer (XVI) is isolated by flash chromatography. Hydrogenolitic deprotection of the benzyl ether of (XVI) gives alcohol (XVII).