73(P-57) 植物ステロール側鎖生合成機構の解析 : C-28位における反応の立体化学(ポスター発表の部)
スポンサーリンク
概要
- 論文の詳細を見る
A typical plant C_<29>-sterol, sitosterol, is biosynthesized from a steroidal 24-ene precursor in reactions involving two methylation steps by attack of S-adenosylmethionine, via 24-methylenecholesterol, isofucosterol and 24-ethyldesmosterol. The present studies are focused to elucidate reaction mechanisms with special reference to stereochemical nature of the reactions at the C-28 position in higher plants. First, the stereochemical features of the second methylation, namely, of the conversion from 24-methylenecholesterol to isofucosterol has been investigated. Feeding studies of stereoselectively synthesized [28E-^2H]- and [28Z-^2H]-24-methylenecholesterols to cell culturs of Morus alba followed by ^2H-NMR analysis of the resulting isofucosterol established that this methylation proceeds in such a manner that addition of the methyl group and proton loss occur on opposite faces of the original Δ^<24(28)>-double bond (designated as "trans-mechanism"). Second, the mechanism of the double bond isomerization from Δ^<24(28)> to Δ^<24(25)>, i.e., the conversion of isofucosterol to 24-ethyldesmosterol, was investigated by feeding [28-^<13>C, 28-^2H] doubly labeled isofucosterol to cell cultures of Oryza sativa and Morus al, and ^2H-decoupled ^<13>C, ^1H shift correlation NMR analysis of the biosynthesized sitosterol. The {^1H}{^2H}HMQC spectrum revealed that the deuterium of isofucosterol stereospecifically becomes pro-R-^2H at C-28 of sitosterol, thus establishing that the double bond migration takes place in a syn-S_E2' manner wherein the pro-S-hydrogen at C-28 of sitosterol is introduced from the 28-si face of isofucosterol. Third, steric course of the methyl donation from S-adenosylmethionine in the biosynthesis of clerosterol [(24S)-ethylcholesta-5,25-dien-3β-ol] has been elucidated. In this methylation, a C-24 cationic species arising from the methyl transfer at the C-28 position of a 24-methylene-sterol undergoes migration of C-25 hydrogen to C-24 with concomitant elimination of hydrogen at C-26 to form clerosterol. Feeding of [28Z-^2H]- and [28E-^2H]-24-methylenecholesterols to hairy roots of Ajuga reptans var. atropurpurea and ^2H-NMR analysis of clionasterol obtained by partial hydrogenation of the biosynthesized clerosterol have revealed that the methylation takes place from 28-si face (anti to the migrating H-25). This work is the first to determine the steric course of the methyl transfer in the conversion of C_<28>-to C_<29>-sterol. In Ajuga hairy roots, the transfer of the methyl group in the conversion of C_<27>- to C_<28>-sterol, e.g., from desmosterol to codisterol (24β-methyl-Δ^<25>-cholesterol), proceeds from the 24-si face of Δ^<24(25)> double bond. Therefore, it can be suggested that the methyl group of S-adenosylmethionine should be held in the backside of the Δ^<24(25)> and Δ^<24(28)> double bond in both methyl transfer reactions.
- 天然有機化合物討論会の論文
- 2002-09-01
著者
関連論文
- 72(P-55) ステロール生合成におけるΔ^オレフィン還元反応の立体化学(ポスター発表の部)
- 32 コール酸生合成におけるステロイド側鎖切断反応(β-酸化)の立体化学(口頭発表の部)
- NON-STEREOSPECIFIC FORMATION OF 3α, 7α, 24-TRIHYDROXY-5β-CHOLESTAN-26-OIC ACID DURING CHENODEOXYCHOLIC ACID BIOSYNTHESIS
- Non-stereoselective Formation of 3α, 7α, 12α, 24-Tetrahydroxy-5β-cholestan-26-oic Acid during Cholic Acid Biosynthesis
- Stereochemistry of Hydrogen Addition to C-25 of Desmosterol by Sterol-Δ^-Reductase of Rat Liver Homogenate
- IDENTIFICATION OF 27-NOR-3α, 7α, 12α-TRIHYDROXYCOPROSTAN-24-ONE APPARENTLY DERIVED FROM 3α, 7α, 12α-TRIHYDROXY-24-OXOCOPROSTANOIC ACID, A POSTULATED INTERMEDIATE OF BILE ACID BIOSYNTHESIS
- Formation of 9,25-Cyclofernane by Reductive Homoallylic Cyclization of Fern-9(11)-en-25-ol Mesylate
- Annonaceous Acetogenins from the Seeds of Annona squamosa.Adjacent Bis-tetrahydrofuranic Acetogenins
- A NOVEL STEROIDAL SAPOGENIN, POGOSTEROL FROM VERNONIA POGOSPERMA
- 75 バンレイシ科植物Annona squamosaのビステトラヒドロフランアセトゲニン類の構造(ポスター発表の部)
- 植物ステロール側鎖の生合成機構の精密解析
- 26,27-DIETHYL-1α,25-DIHYDROXYVITAMIN D_3 AND 24,24-DIFLUORO-24-HOMO-1α,25-DIHYDROXYVITAMIN D_3 : HIGHLY POTENT INDUCER FOR DIFFERENTIATION OF HUMAN LEUKEMIA CELLS HL-60(Communications to the Editor)
- SYNTHESIS OF β-OXO THIOL ESTERS RELATED TO BILE ACID BIOSYNTHESIS
- P-1 Acaterinの生合成研究 : Dehydroacaterin reductaseの遺伝子クローニングとその反応機構(ポスター発表の部)
- バンレイシ科植物Annona reticulata種子から得た新規ビステトラヒドロフランアセトゲニンの構造 : 有機化学・天然物化学
- P-61 非直結型ビステトラヒドロフランアセトゲニンの立体化学について(ポスター発表の部)
- Squamosten-A, a Novel Mono-tetrahydrofuranic Acetogenin with a Double Bond in the Hydrocarbon Chain, from Annona squamosa L.
- テトラヒドロフランアセトゲニン類の構造解析--プレカ-サ-イオンスキャン法の適用
- P-35 ゴマノハグサ目植物の腺毛分泌物の化学成分研究(ポスター発表の部)
- 73(P-57) 植物ステロール側鎖生合成機構の解析 : C-28位における反応の立体化学(ポスター発表の部)
- 23 高等植物における24-メチルステロール側鎖の生合成機構の解析(口頭発表の部)
- カイコの休眠卵に見いだされた未同定エクジステロイド, 特に3-エピエクジステロイドの精製と構造解析について
- Annonaceous Acetogenins from the Seeds of Annona squamosa.Non-adjacent Bis-tetrahydrofuranic Acetogenins
- テトラヒドロフランアセトゲニン類の構造解析-プレカーサーイオンスキャン法の適用-