Presqualene alcohol, squalene, and sterol biosynthesis from bifarnesol

To cast light on the overall biosynthetic conversion of farnesol pyrophosphate to presqualene alcohol pyrophosphate (PSA), the biochemical precursor of squalene as well as all sterols, radiolabeled bifarnesol (1) was prepared and fed toGibberella fujikuroi. The diol (1), acting as a surrogate for a previously suggested phosphorylated version of1, was converted to radiolabeled presqualene alcohol and squalene, as well as various sterols, including lanosterol and24-β-methylcholesta-5,7,9(11),22-tetraen-3β-ol, previously isolated from the same fungus. The results are interpreted to imply that a phosphorylated version of1 may act as a bone fide intermediate in the biosynthesis of PSA, thereby rendering unlikely any type of concerted farnesyl/presqualene pyrophosphate change.