Antimelanogenic properties of glycerol-linked hexadecatetraenoic acid derivatives isolated from Ulva prolifera.

Ethanol extracts from four species of green algae were comparatively evaluated for antimelanogenic activity using B16F10 mouse melanoma cells. The extract derived from Ulva prolifera demonstrated the strongest inhibitory effect on melanin synthesis and was thus selected for further investigation to isolate and identify its bioactive constituents. Through sequential chromatographic techniques, two active compounds-1-hexadecatetraenoylglycerol and 1-hexadecatetraenoyl-3-β-D-galactopyranosylglycerol-were isolated and structurally characterized via NMR and mass spectrometric analyses. Notably, hexadecatetraenoic acid alone did not exhibit antimelanogenic activity under the same experimental conditions, whereas its glycerol-conjugated form, 1-hexadecatetraenoylglycerol, significantly suppressed melanin production. Additionally, neither the ethanol extract of U. prolifera nor the isolated compounds directly inhibited tyrosinase activity, suggesting that they may influence melanogenesis through indirect mechanisms. These results suggest that the molecular configuration of fatty acids plays an important role in antimelanogenic activity and highlight the potential of lipid components from U. prolifera as functional antimelanogenic agents.