Stephacidin

Stephacidin A and B are antitumor alkaloids isolated from the fungus Aspergillus ochraceus [1] that belong to a class of naturally occurring 2,5-diketopiperazines.

[2] This unusual family of fungal metabolites are complex bridged 2,5-diketopiperazine alkaloids that possess a unique bicyclo[2.2.2]diazaoctane core ring system and are constituted mainly from tryptophan, proline, and substituted proline derivatives where the olefinic unit of the isoprene moiety has been formally oxidatively cyclized across the α-carbon atoms of a 2,5-diketopiperazine ring.

[4] Avrainvillamide, which contains a 3-alkylidene-3H-indole 1-oxide function, was identified in culture media from various strains of Aspergillus and is reported to exhibit antimicrobial activity against multidrug-resistant bacteria.

[5] The avrainvillamide and stephacidins family of structurally complex anticancer natural products are active against the human colon HCT 116 cell line.

[6] The signature bicyclo[2.2.2]diazaoctane ring system common to these alkaloids has inspired numerous synthetic approaches.