Stereospecific Synthesis of 24-Propylcholesterol Isolated from the Texas Brown Tide

The alga that causes the ‘Texas brown tide’, Aureoumbra lagunensis, contains 24-propylcholesterol, a potentially useful biomarker for this organism. The stereochemical configuration at C-24 was determined through synthesis using the Johnson orthoester Claisen rearrangement. Both (24R)- and (24S)-24-propylcholesterol, as well as (24R)- and (24S)-Δ22 24-propylcholesterol, were synthesized and characterized. The naturally occurring isomer was found to be (24R)-24-propylcholesterol.