New antibacterial 2-bromopyrrole-2-aminoimidazolinone alkaloids, 10E-dispacamide B and (+)-10E-dispacamide D, from a sponge Agelas nakamurai (Hoshino, 1985).

Continued chemical investigation of the sponge Agelas nakamurai led to the isolation of two new 2-bromopyrrole-2-aminoimidazoline alkaloids, 10E-dispacamide B (1) and (+)-10E-dispacamide D (2), together with their known 10Z-isomers, dispacamide B (3) and dispacamide D (4). The structures of the new metabolites were elucidated through comprehensive spectroscopic analyses, including 2D NMR experiments, along with the assistance of a single-crystal X-ray diffraction (SC-XRD) analysis of compound 3. Biological evaluation revealed that the newly identified alkaloids, 10E-dispacamide B (1) and (+)-10E-dispacamide D (2), exhibited stronger antibacterial activity than their corresponding 10Z-isomers, 3 and 4. In addition, a plausible biosynthetic pathway for the formation of both the 10E and 10Z isomers 1-4 from laughine was proposed. The occurrence of both 10E- and 10Z-isomers highlights the remarkable biosynthetic versatility of this sponge and underscores its potential as a valuable source of structurally diverse and biologically active natural products.