Calothrixins A and B, Novel Pentacyclic Metabolites from Calothrix Cyanobacteria with Potent Activity against Malaria Parasites and Human Cancer Cells

Abstract

Cell extracts from photoautrophic cultures of two cyanobacterial Calothrix isolates inhibited the growth in vitro of a chloroquine-resistant strain of the malaria parasite, Plasmodium falciparum, and of human HeLa cancer cells, in a dose-dependent manner. Bioassay-directed fractionation of the extracts led to the isolation and structural characterization of calothrixins A (1) and B (2), pentacyclic metabolites with an indolo[3,2- j]phenanthridine ring system unique amongst natural products, which exert their growth-inhibitory effects at nanomolar concentrations. Show more