Spiroindimicins A-D: new bisindole alkaloids from a deep-sea-derived actinomycete.

A PCR-based screening approach led to the identification of a deep-sea-derived Streptomyces sp. SCSIO 03032 capable of producing new bisindole alkaloids spiroindimicins A–D (1–4). Structural elucidation of these compounds revealed the presence of unusual [5,6] or [5,5] spiro-ring containing skeletons. Spiroindimicins B–D (2–4) with a [5,5] spiro-ring exhibited moderate cytotoxicities against several cancer cell lines.