Identification of 24-n-propylidenecholesterol in a member of the Foraminifera

We report a study of the sterols produced by the thecate allogromid foraminiferan, Allogromia laticollaris, grown in culture. Gas chromatographic retention time, together with mass spectrometric fragmentation patterns of trimethysilyl and acetate derivatives enabled us to assign a suite of C27-C30 sterols. Two C30 sterols were identified as (24E)-n-propylidenecholesterol and its 24Z isomer by direct comparison with an authentic standard. The C30 sterols were not detected in the two algae, Isochrysis galbana and Dunaliella tertiolecta, used as a food source for the A. laticollaris, consistent with previous analysis of these organisms. The assignment of (24E)-n-propylidenecholesterol was confirmed using 600 MHz 1H nuclear magnetic resonance (NMR) spectroscopy. The result has relevance as to how we might interpret fossil sterane distributions.