Semisynthesis: Treatment of camptothecin (XI) with tert-butylhydroperoxide in the presence of FeSO4, conc. H2SO4 and acetic acid in water gives (S)-7-methylcamptothecin (XII). Mannich reaction of compound (XII) with isopropylamine hydrochloride in DMSO as a formaldehyde source gives CKD-602.
Radical hydroxymethylation of camptothecin (I) by means of MeOH in the presence of H2O2 and FeSO4 provided (II). Subsequent heating of alcohol (II) in acetic acid gave rise to 7-formylcamptothecine (III). Finally, condensation of aldehyde (III) with O-t-butylhydroxylamine afforded the corresponding oxime.
Total synthesis: Reaction of ethyl acetopyruvate (I) with triethyl orthoformate gives compound (II), which is then treated with cyanoacetamide to yield 3-cyano-4-methyl-6-(carbethoxy)-2(1H)-pyridone (III). The reaction of (III) with methyl acrylate (A) gives compound (IV), which is sequentially submitted to decarboxylation, ketalization and treatment with diethylcarbonate, giving the functionalized tetrahydroindolizine (V). Ethylation of (V) followed by reduction in the presence of acetic anhydride gives the amide (VI), which is reacted with sodium nitrite, refluxed in CCl4, hydrolyzed and acidified to give the tricyclic compound (VII). The DIBAL reduction of (VII) and subsequent elimination of the hydroxyl group gives the cyclic enol ether (VIII). Asymmetric dihydroxylation of compound (VIII) with (DHQD)2PHAL, K2OsO4 and K3Fe(CN)6 in t-BuOH gives the diol (IX). The oxidation and deketalization of compound (IX) gives (S)-hydroxylactone (X). Finally, Friedlander condensation of the lactone (X) with 3-[N-isopropyl-N-(carbobenzyloxy)amino]-1-(2-aminophenyl)propan-1-one (B) followed by deprotection gives CKD-602.