Diketopiperazine alkaloids from a mangrove rhizosphere soil derived fungus Aspergillus effuses H1-1

Effusin A (1), a spirobicyclic N,O-acetal derivative with an unprecedented 3',3a',5',6'-tetrahydrospiro-[piperazine-2,2'-pyrano[2,3,4-de]chromene] ring system, and a spiro-polyketide-diketopiperazine hybrid dihydrocryptoechinulin D (2) were isolated from a mangrove rhizosphere soil derived fungus, Aspergillus effuses H1-1. Their structures were determined by detailed spectroscopic analysis. Effusin A (1) and dihydrocryptoechinulin D (2) occurred as racemates, the enantiomers of which were separated and characterized by online HPLC-ECD analysis and their absolute configurations were determined by the solution TDDFT ECD calculation approach. The cytotoxic effects of 1 and 2 were preliminarily evaluated and 2 showed potent activity on P388 cells with an IC50 value of 1.83 mu M. The target of racemic 2 was also investigated and the (12R,28S,31S)-2 enantiomer showed selectivity against topoisomerase I.