Threo tetrahydro

Chemical Name 1-(L-Threo-3 6-diamino-4-hydroxyhexanoic acid)-6-[L-2-(2-amino-1,4,5,6-tetrahydro-4-pyrimidinyl)glycine] viomycin... 

The conformations of the 2-oxo-tetrahydro-l,3-oxazines obtained from phosgene and the isomeric 3-amino-2,3-diphenylpropanols were used by Fodor et al. as an ingenious criterion for the configurational determination of the aminopropanols.13,14 The erythro form yielded an oxazinone that showed optical activity 4-8 times stronger than that from the threo form. 

Addition of bromine in dichloromethane or of thioacetic acid in ethanol onto the methylene group of 9-arylidene and 9-carboxymethylene moieties of 6,7,8,9-tetrahydro-4//-pyrido[l,2-a]pyrimidines 546 stereoselectively gave 9-substituted 6,7,8,9-tetrahydro derivatives 547 and 548, respectively, at ambient temperature (Scheme 34) (90JHC247). Addition was also stereoselective with respect to the C(9) and C(9)—C centers, giving the erythro diastereomers as the primary products, which may then undergo epimerization to the threo isomers. The structure and epimerization of the products were studied by H and l3C NMR spectroscopy and by molecular mechanics calculations. 

The tetrahydro-l,3-oxazin-2-one (372) is prepared through the cyclization of the threo form of hydroxycarbamate (371) in contact with mesyl chloride, conversely the erythro isomer is O-sulfinated without undergoing cyclization. The removal of an A-Boc group under basic conditions is unusual, and it is proposed that the selective cyclization of the threo isomer occurs because, in its lowest energy conformation, the proximity of the ethoxycarbonyl group and the mesyloxy unit potentiates the ionization of the latter. Once formed, the mesyloxy anion assists deprotonation of the Boc group and hence the cyclization to the oxazine (Scheme 100) <87H(26)64i, 88H(27)667>. 

All four stereoisomers of 4-amino-(2-hydroxymethyl) tetrahydro-furan 4-carboxylic acid (a 2-C-hydroxymethyl pentonic acid derivative) (25) have been synthesized from D-glucose or D-ribose derivatives as outlined in Scheme 9, the threo-isomers spontaneously forming 6-lactones the 2S,4S (D-erythro) isomer was then shown to be the one previously detected in an acid hydrolysate of di abeti c urine. ... 

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