Identification and Spatial Distribution of Long-Chain Alkyl Sulfates from the Solitary Ascidian Ascidiella aspersa

Long-chain alkyl sulfate 1, three new derivatives 2−4, and (−)-loliolide-3-sulfate (7) were isolated from the solitary ascidian Ascidiella aspersa. The structures of compounds 1−4 were elucidated by NMR spectroscopy, HRESI-MS/MS, and chemical degradation. Disulfates 1 and 4 were localized predominantly in the intestinal tissue, whereas monosulfates 2 and 3 were enriched in the gut contents and intestinal lumen. Although monosulfates were minor metabolites compared with the major disulfate 1, they were released into seawater in substantially larger amounts. Mass spectrometry imaging confirmed the distinct spatial distribution of disulfates within the intestinal tissue and monosulfates in the gut contents. Furthermore, compound 1 was contained in larvae and juveniles but was not detected from egg extracts, suggesting that 1 appears after fertilization and larval development. Together, these findings reveal a clear functional differentiation between mono- and di-sulfated alkyl sulfates, suggesting that disulfates are selectively retained as endogenous metabolites, whereas monosulfates are preferentially released into the surrounding seawater. This study provides the first evidence for tissue-specific localization and differential release of long-chain alkyl sulfates, offering new insights into their ecological and physiological functions in ascidians.