Spectral and photophysical properties of the δ-carboline anhydrobase (N1-methyl-5H-pyrido[3,2-b]indole)

Access to γ-Carbolines: Synthesis of Isocryptolepine

A new method to synthesize γ-carboline derivatives has been developed starting from 3,5-dibromo-4-pyridinamine by monoarylation using the Suzuki-Miyaura cross-coupling reaction followed by the base-mediated ring closure to pyrrole formation. Synthesis of a series of γ-carboline derivations from the 4-brominated γ-carboline 4a has been achieved by employing various coupling reactions and N-alkylations. This method has been applied for the synthesis of the antimalarial and anticancer natural product isocryptolepine. The photophysical properties of novel γ-carboline derivations are also reported.

Interaction of β-Lactam Carbenes with Aryl Isonitriles: An Unprecedented Rearrangement of 2-Azetidinonylidene Indoles to δ-Carbolinones

The reaction of beta-lactam carbenes with aryl isonitriles proceeded in a novel [2 + 2] fashion to give high yields of 2-azetidinonylidene indoles 4, which underwent an unprecedented rearrangement to furnish 4-arylimino-delta-carbolin-2-ones 5 in almost quantitative yields. Acid catalyzed rearrangement and the subsequent hydrolysis of 2-azetidinonylidene indoles 4 produced two types of delta-carbolin-2,4-diones 10 and 11, respectively, in good to excellent yields. The photophysical study showed that both delta-carbolin-2,4-diones 10 and 11 are highly fluorescent with the fluorescent quantum yields being up to 0.43.