Psammocindoles A–C: Isolation, Synthesis, and Bioactivity of Indole-γ-lactams from the Sponge Psammocinia vermis

Psammocindoles A–C (1–3), a new class of indole alkaloids, were isolated from a Psammocinia vermis sponge. By combined spectroscopic analyses, the structures of these compounds were determined to be the indole-γ-lactams derived from three amino acid residues. In addition, an enantiomer psammocindole D (4), and the N-lactam isomers isopsammocindoles A–D (5–8) were also synthesized. These natural products and synthetic analogues were found to significantly stimulate adiponectin secretion in human bone marrow mesenchymal stem cells.