1) The cyclization of meso-2,6-bis(benzyloxycarbonylamino)heptanedioic acid (I) with PCl5 gives the corresponding bis oxazolidinedione (II), which is treated with tert-butyl carbazate (III) yielding the bis hydrazide (IV). Enzymatic hydrolysis of (IV) with Streptomyces sapporonensis affords the (S)-monoacid (V), which is selectively protected with benzyl chloroformate and copper chelate (VI). A second protection reaction of (VI) with tert-butoxycarbonyl anhydride gives the amino protected acid (VII) , which is condensed with D-alanine benzyl ester (VIII) by means of isobutyl chloroformate to afford the acylated D-alanine (IX). Elimination of the benzyloxycarbonyl groups of (IX) by hydrogenolysis yields compound (X) with a free amino group, which is condensed with N-heptanoyl-D-glutamic acid 1-benzyl monoester (XI) to give the protected FK-565 precursor (XII). Finally, this compound is deprotected with trifluoroacetic acid and sodium periodate.
2) The methylation of meso-2,6-bis(benzyloxycarbonylamino)heptanedioic acid (I) with diazomethane gives the corresponding dimethyl ester (XIII), which is submitted to a selective hydrolysis with a protease type VIII enzyme yielding the monoester (XIV). The cyclization of (XIV) with PCl5 affords the oxazolidinedione (XV), which is condensed with D-alanine 4-nitrobenzyl ester (XVI) to give compound (XVII) with a free amino group that is condensed with D-glutamic acid monoester (XI) affording the fully protected FK-565 derivative (XVIII), which is first debenzylated by hydrogenolysis to methyl ester (XIX), and finally hydrolyzed with NaOH.