New Antimalarial and Antimicrobial Tryptamine Derivatives from the Marine Sponge Fascaplysinopsis reticulata

Chemical study of the CH₂Cl₂-MeOH (1:1) extract of the sponge Fascaplysinopsis reticulata collected in Mayotte highlighted three new tryptophan derived alkaloids, 6,6'-bis-(debromo)-gelliusine F (1), 6-bromo-8,1'-dihydro-isoplysin A (2) and 5,6-dibromo-8,1'-dihydro-isoplysin A (3), along with the synthetically known 8-oxo-tryptamine (4) and the three known molecules from the same family, tryptamine (5), (E)-6-bromo-2'-demethyl-3'-N-methylaplysinopsin (6) and (Z)-6-bromo-2'-demethyl-3'-N-methylaplysinopsin (7). Their structures were elucidated by 1D and 2D NMR spectra and HRESIMS data. All compounds were evaluated for their antimicrobial and their antiplasmodial activities. Regarding antimicrobial activities, the best compounds are (2) and (3), with minimum inhibitory concentration (MIC) of 0.01 and 1 µg/mL, respectively, towards Vibrio natrigens, and (5), with MIC values of 1 µg/mL towards Vibrio carchariae. In addition the known 8-oxo-tryptamine (4) and the mixture of the (E)-6-bromo-2'-demethyl-3'-N-methylaplysinopsin (6) and (Z)-6-bromo-2'-demethyl-3'-N-methylaplysinopsin (7) showed moderate antiplasmodial activity against Plasmodium falciparum with IC₅₀ values of 8.8 and 8.0 µg/mL, respectively.