Synthesis of Didemnolines A-D, N9-Substituted #beta#-Carboline Alkaloids from the Marine Ascidian Didemnum sp.

摘要

Didemnolines A-D (1-4) were synthesized and their structures were confirmed through comparisons of data for the synthetic material with those obtained for natural 1-4. The synthesis of didemnolines A (1) and C (3) involved the coupling of 1-[(benzyloxy)methyl]-4-chloromethyl-5-(thiomethyl)imidazole (6) with 7-bromo-#beta#-carboline (5), while didemnolines B (2) and D (4) were formed through the analogous coupling of 6 with norharmon (7). Intermediate 6 was efficiently prepared from 1-[(benzyloxy)methyl]-2,4,5-tribromoimidazole using a sequential one-pot halogen-metal exchange reaction and 7-Br-#beta#-carboline was synthesized using a new approach.