Effects of triparanol and AY‐9944 upon sterol biosynthesis inChlorella

The growth rates of three species ofChlorella were inhibited by triparanol and AY‐9944.Chlorella emersonii was noticeably more resistant to both inhibitors than the other species. A large number of sterols were isolated and identified in inhibited cultures. Ca. 18 of these were identified from nature for the first time. Triparanol resulted in inhibition of the removal of the 14α methyl group. It also inhibited the second alkylation of the side chain and, in one species, strongly inhibited the Δ8 → Δ7 isomerase reaction. InC. ellipsoidea, triparanol also inhibited Δ14‐reductase and Δ7‐reductase. The introduction of the Δ22 double bond was inhibited by both drugs. The effect of AY‐9944 was similar to that of triparanol inC. emersonii, but it was an extremely effective Δ14‐reductase inhibitor inC. ellipsoidea. These various types of inhibition of sterol synthesis indicate a lack of specificity of both drugs inChlorella and suggest that primitive plants such as these may be valuable as test organisms in an evaluation of the activity of potential inhibitors of sterol biosynthesis.