Role of cycloartenol in the formation of phytosterols. Biosynthesis of sitosterol-19-2H in deuterium oxide germinated peas

Biosynthesis of tetrahymanol by Tetrahymena pyriformis: mechanistic and evolutionary implications

“…It was proposed that cycloartenol (11) is the precursor of phytosterols.20,21 Indeed, evidence was obtained that in peas cycloartenol or a C-19 carbanion is an intermediate in the elaboration of sitosterol. 22,23 In many organisms (e.g., plants, etc.) 2(3)-oxidosqualene can be cyclized to the pentacyclic hopenyl cation.…”

“…Encouraged by these results, we undertook the synthesis of deuterated model compounds suitable for comparison with tetrahymanol. We chose 3 -( 21) and 3/3-deuterio-4,4-dimethyl-5a-cholestanes (22) as models.42,43 Our rationale for selecting these compounds was that rings A and B of the 4,4-dimethyl-5a-cholestane are structurally and environmentally analogous to rings A and B of tetrahymanol. Therefore, it was considered likely that the chemical shifts of the 3 -( 21) and 3/3deuterons (22) of the model 4,4-dimethylcholestanes and of their 3-deuteriotetrahymanol counterparts would be very similar, if not identical.…”

“…Hydrogenolysis (LiAlH4) of the 2a-tosyl ester (24b) should therefore yield the desired product. Thus, deuterioboration of the We have also attempted to obtain the 3/3-deuterio 22 via hydrogenation of the 3-deuterio-A2-olefin 23b. However, when an ethyl acetate solution of 23b was hydrogenated over platinum oxide, the reaction proceeded only in part in the expected manner from the a side of the molecule.…”

Biosynthesis of phytosterols in the pea. Mode of incorporation of carbon-2 hydrogen atoms of mevalonic acid into sitosterol

“…The feasibility of a process not involving a 14 (15) doublebond intermediate in plant sterol biosynthesis was enhanced by the isolation of 5a-stigmasta-8 ( 14),22-diene-30-ol from rayless goldenrod (Aplopappus heterophyllus).10 In essence, this brought to mind the possibility that the formation of plant sterols might involve an intermediate having an 8(14) double bond. It may be recalled that based on the concepts of Gautschi and Bloch, 11 Fried et al 12 and Schroepfer et al 13 have suggested that the biosynthesis of cholesterol proceeds via an 8( 14)-olefinic intermediate obtained in the course of the removal of the 14a-methyl group.…”

“…The recrystallized 11 and 12 showed mp 146-148 °C; MS m/e 488 (M+, 14), 470 (M -18, 5), 445 (M -43, 14), 347 (M -141,6), 329 [M -(141 + 18), 10], 294 (M -194, 22), 293 (M -195, 100), 292 (M -196, 100), 253 (M -235,100); NMR 0.788 (s, 3 H, 18-CH3, caled 0.859), 1.020 (s, 3 H, 19-CH3, caled 0.833), 0.938 (d, J = 6.5 Hz, 3 H, 21-CH3), 0.810 (d, J = 6.5 Hz, 3 H, 26-CH3), 0.825 (d, J = 6.5 Hz, 3 H, 27-CH3), 0.920 (d, J = 6.0 Hz, 3 H, 29-CH3), 2.000 (s, 3 H, 3/3-OAc), 4.68 (m, 1 , 3a-H).…”