The chloroform/methanol extract of the red alga, Laurencia papillosa, collected from the Red Sea in Saudi Arabia, was found to contain two cholestane derivatives: 3α, 6α-dihydroxy-5β-cholestan-12-one (1) and the known, 6β-hydroxycholest-4-en-3-one (2), which was isolated separately in a pure form for the first time. In addition to these compounds, a new aldehyde derivative, (E)-2-{(E) tridec-2-en-2-yl} heptadec-2-enal (3), was isolated. The structures of all compounds were established based on extensive spectroscopic (1D and 2D NMR, UV, IR) and mass spectrometric studies. All compounds, except 2, were tested for their antifungal activity. Significant activities were associated with 1 and 3 against Candida albicans, Aspergillus fumigatus, and A. flavus.
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