Chemoenzymatic syntheses of each stereoisomer of (4,5)-epoxy-(2E)-hexenoates

Synthesis of γ- and δ-Lactone Natural Products by Employing a trans–cis Isomerization/Lactonization Strategy

“…Alkakine hydrolysis of (S)-20 followed by acid treatment provided the desired acid (S)-21, which was subjected to lactone formation reaction without further purification. The trans-structure of (S)-21 was confirmed by Deprotection of the reported (4S,5R)-and (4R,5S)-11 3) by the same way as the preparation of (±)-13 from (±)-11 gave (4S,5R)-13 (86% yield) and (4R,5S)-13 (74% yield), respectively. Alkakine hydrolysis of (4S,5R)-13 and (4R,5S)-13 followed by acid treatment provided the desired acids (4S,5R)-23 and (4R,5S)-23, respectively, which were subjected to lactone formation reaction without further purification.…”

“…The AlCl 3 mediated debenzylation 3) of (±)-11 in m-xylene gave (±)-(4,5-anti)-4,5-dihydroxy-(2E)-hexenoate (13) in 66% yield, which was treated with benzaldehyde in the presence of p-toluenesulfonic acid (p-TsOH) to afford a mixture of acetals [(±)-14 and (±)-15] in 83% yield. Treatment of this mixture with sodium cyanoborohydride [Na(CN) BH 3 ] gave (±)-(4,5-anti)-5-benzyloxy-4-hydroxy-(2E)-hexenoate (16) (78% yield) and (±)-11 (13% yield).…”

“…The reaction mixture was evaporated to give a residue, which was dissolved with a mixed solvent (Et 2 O (5.0 mL) and AcOEt (2 mL)). The organic solvent soluble part by filtration was dried over MgSO 4 and evaporated to afford a residue, which was chromatographed on silica gel (20 g, CHCl 3 …”

“…The compound (±)-17 was synthesized from the reported (±)-11 3) as shown in Chart 3. The AlCl 3 mediated debenzylation 3) of (±)-11 in m-xylene gave (±)-(4,5-anti)-4,5-dihydroxy-(2E)-hexenoate (13) in 66% yield, which was treated with benzaldehyde in the presence of p-toluenesulfonic acid (p-TsOH) to afford a mixture of acetals [(±)-14 and (±)-15] in 83% yield.…”

Determination of the Absolute Stereostructure of seco-Macrosphelide E Produced by a Fungal Strain from a Sea Hare.

“…in phosphate buffer solution gave the (4R,5S)-5-acetoxy ester 5 (Ͼ99% ee, 48% yield) and the (4S,5R)-5-hydroxy ester 6 (Ͼ99% ee, 44% yield), and methanolysis of (4R,5S)-5 provided the (4R,5S)-6 in 84% yield. 4) The key compound in the synthesis of (ϩ)-1 and (ϩ)-3 is (4R,5S)-4-benzyloxy-5-silyloxy-2(E)-hexenoic acid 7 and this compound was also used for the synthesis of 2 or 4 as a starting material. Condensation of carboxylic acid (4R,5S)-7 and commercially available (3R)-hydroxy butanoate 8 via the Keck procedure 5) MS) of (3R,8R,9S,14R,15S))-2 and (3S,8R,9S,14R,15S)-4 quite resembled those of the natural product 2, respectively, while both retention times of (3R,8R,9S,14R,15S)-2 (t R ϭ19.3 min) and (3S,8R,9S,14R, 15S)-4 (t R ϭ25.8 min) by mean of HPLC (column; CHIRAL-CEL OD (0.46ϫ25 cm), solvent; n-hexane-EtOH (10 : 1); detection; 254 nm) were quite different.…”