合成路线1

Chlorination of 2-nitro-4,5-dimethoxybenzoic acid (I) by using oxalyl chloride and DMF provides acid chloride (II), which is subsequently coupled to hydroxyproline methyl ester (III) to yield amide (IV). Catalytic hydrogenation of the nitro group of (IV), followed by intramolecular cyclization leads to the tricyclic lactam (V). In order to protect the lactam NH of (V), the hydroxyl group is first converted into the silyl ether (VI), which is further treated with trimethylsilylethoxymethyl chloride and NaH to give the SEM-lactam (VII). Selective O desilylation of (VII) is accomplished by means of tetrabutylammonium fluoride, providing alcohol (VIII). Oxidation of (VIII) under Swern reaction conditions gives rise to ketone (IX).