Synthesis of new lavendamycin analogues

Friedländer reaction between methyl acetoacetate and 2,4-diaminobenzaldehyde provided quinoline 11. Subsequent tosylation, reduction, silylation, and then oxidation led to aldehyde 15. The latter was subjected to a Pictet–Spengler reaction with tryptophan methyl ester that yielded product 16, and then desilylation gave the lavendamycin analogue 17. This compound was oxidized by Dess–Martin periodinane, and the cyclized derivative 18 was obtained via a hemiaminal intermediate. The same sequence from 2,4-diamino-5-methoxybenzaldehyde or from (2,4-diaminophenyl)propan-3-one led to compounds 30 and 31, or 40 and 41, respectively.