8 ジアセトングルコースを鋳型とする不斉転写(口頭発表の部)

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Carbohydrates are important sources of chirality in organic synthesis. We recently became aware of possible stereocontrol elements in which the intrinsic molecular architecture of a carbohydrate may serve as a template for chirality transcription irrespective of individual chiral carbons. Oxidation of diacetone-D-glucose affords 1,2:5,6-di-O-isopropylidene-α-D-ribo-hexos-3-ulose 1. The molecular architecture of 1 can be regarded as a sort of C_2 symmetric cyclopentanone, having an α-oriented bulky 1,2-O-isopropylidene protecting group and a β-oriented large substituent at C-4 in the five-membered furanose ring. Thus, α- and β-substituents introduced into the C-3 carbonyl group must sterically interact with these two bulky substituents. These steric interactions may be promising elements for stereochemical control for the reactions on the chiral template 1. In the present studies, the β-substituents were substituted vinyl groups introduced into the C-3 carbonyl group of 1, and the derived hydroxyl group was modified into the suitable α-substituent. Diastereoselective reaction due to the single steric interaction between the β-oriented vinyl group and the bulky substituent at C-4 was demonstrated in the OsO_4 oxidation of 13 and 16, from which all four diastereoisomers of monodeuterated glycerol were synthesized. The inherent antiparallel double repulsion as illustrated in the introductory figure can fix the conformation between the β-substituent and the α-substituent at C-3. Thus, the intramolecular reaction such as Claisen-type rearrangement and [2,3]-Wittig rearrangement between these substituents may well proceed highly diastereoselectively in such a way that one particular face of the double bond is involved. Usefulness of this stereocontrol elements was demonstrated in the enantioselective syntheses of D- and L-alanine 24 and 25, chiral glycines 26 and 27 as well as 3-isopropylmalic acid 32. This approach was applied to the stereochemical studies on the decarboxylation reaction of 3-isopropylmalate dehydrogenase from thermophilic bacteria Thermus thermophilus HB-8.
天然有機化合物討論会の論文
1991-09-07

8 ジアセトングルコースを鋳型とする不斉転写(口頭発表の部)

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