Antimicrobial Diterpene Alkaloids from an Agelas citrina Sponge Collected in the Yucatán Peninsula.

Three new diterpene alkaloids, (+)-8-epiagelasine T ( 1 ), (+)-10-epiagelasine B ( 2 ), and (+)-12-hydroxyagelasidine C ( 3 ), along with three known compounds, (+)- ent -agelasine F ( 4 ), (+)-agelasine B ( 5 ), and (+)-agelasidine C ( 6 ), were isolated from the sponge Agelas citrina , collected on the coasts of the Yucatán Peninsula (Mexico). Their chemical structures were elucidated by 1D and 2D NMR spectroscopy, HRESIMS techniques, and a comparison with literature data. Although the synthesis of (+)- ent -agelasine F ( 4 ) has been previously reported, this is the first time that it was isolated as a natural product. The evaluation of the antimicrobial activity against the Gram-positive pathogens Staphylococcus aureus , Streptococcus pneumoniae , Enterococcus faecalis showed that all of them were active, with (+)-10-epiagelasine B ( 2 ) being the most active compound with an MIC in the range of 1-8 µg/mL. On the other hand, the Gram-negative pathogenes Acinetobacter baumannii , Pseudomonas aeruginosa , and Klebsiella pneumoniae were also evaluated, and only (+)-agelasine B ( 5 ) showed a moderate antibacterial activity with a MIC value of 16 μg/mL.