A highly nitrogen-enriched antibacterial purine derivative from the Vietnamese marine sponge <i>Petrosia</i> sp.

A highly nitrogen-enriched purine derivative, 1,3-dimethyl-8-azaisoguanine (azapetrosia) (1), along with four known compounds, including theophylline (2), 1H-indol-3-carbaldehyde (3), 4-hydroxybenzaldehyde (4), and 4-hydroxy-3-methoxybenzaldehyde (5), was isolated from Petrosia sp. using bioassay-guided isolation. Their structural elucidation was performed using NMR, UV, IR, HRESIMS, and HRESIMS/MS. Azapetrosia was a rare molecule characterised by a distinctive cyclic nitrogen atom linkage. Compound 1 showed significant antibacterial activity against both Gram-positive and Gram-negative bacteria, with IC50 values ranging from 0.59 ± 0.24 to 17.28 ± 2.35 μM. It exhibited the highest potency, with IC50 values of 0.59 ± 0.24 μM against Escherichia coli and 1.28 ± 0.45 μM against Staphylococcus aureus, respectively. These findings underscore Petrosia sp. as a promising source of novel antibacterial compounds, exhibiting significant potential for the development of therapeutic agents targeting drug-resistant bacterial pathogens.