First total synthesis and determination of the absolute configuration of 1-N-methyl-3-methylamino-[N-butanoicacid-3-(9-methyl-8-propen-7-one)-amide]-benzo[f][1,7]naphthyridine-2-one, a novel benzonaphthyridine alkaloid

Abstract The first total synthesis of benzonaphthyridine alkaloid ( 1 ), a unique diazaphenathrene alkaloid isolated from mangrove-derived Streptomyces albogriseolus , was accomplished. The core structure was unequivocally constructed via several key transformations, such as Knoevenagel condensation, Curtius rearrangement, and cyclic carbamate formation–reduction sequence. The chiral unsaturated ketone acid moiety was synthesized from N - tert -butoxycarbonyl- l -glutamic acid gamma- tert -butyl ester ( 15 ). The absolute configuration was determined.