Synthesis of Clausenal, 1,5-Dimethoxycarbazole-3-carbaldehyde and 2,5-Dimethoxycarbazole-3-carbaldehyde

Abstract

Clausenal (1,8-dimethoxycarbazole-3-carbaldehyde) represents the only known naturally occurring 1,8-dioxygenated carbazole alkaloid. However, the structural assignment for clausenal has recently been questioned because of some discrepancies between a synthetic sample and the natural product with respect to NMR data and melting points. Therefore, we have synthesized clausenal as well as two potential structural alternatives (1,5-dimethoxycarbazole-3-carbaldehyde and 2,5-dimethoxycarbazole-3-carbaldehyde) and compared their spectroscopic data with those reported for the isolated natural product. In conclusion from our investigation, we assume that the original structural assignment reported for clausenal most likely is correct.