Glycosylamine hydrolysis

Microbial degradation of validamycin A (8) with a cell suspension of Pseudomonas dentrificans afforded validamine (202) and valienamine (203). Hydrogenolysis of validamycin B, followed by acid hydrolysis, yielded hydroxy validamine (204). Valiolamine (205) was isolated and shown to be a component of validamycin G. ° Biosynthesis of these carba-glycosylamines was extensively studied, and the intramolecular aldol addition of the... 

Compared with the /V-substituted glycosylamines, the l-amino-l-deoxy-2-ketoses are more stable to moist acid atmospheres, but are still heat-labile and decompose rapidly in mild alkali. They exert greater reducing power, although less than reduc-tones. They brown more easily with amino acids. Acid hydrolysis gives much compared with little HMF, but no hexose is recovered, in keeping with the reaction s being irreversible (however, see below). 

The pH (or Ho - see Chapter 3, footnote xi) dependences of the rates of hydrolysis of glycosylamines are bell-shaped, with the maximimum at a pH... 

Figure 1.24 Mutarotation and hydrolysis of glycosylamines, illustrated with N-aryl glucosylamines.

Substances of structures (105) and (106) may be intermediates in the Amadori rearrangement of glycosylamines (104) when this reaction is catalyzed by certain /3-dicarbonyl compounds. Hydrolysis of (106) would give the products of the rearrangement, the V-substituted 1-aniino-l-deoxy-D-fructoses (109). Hodgehas obtained some evidence for the existence of intermediate compounds in the Amadori rearrangement he formulated these as the branched-chain amino ketoses (78, X = iV-alkyl or V-aryl). 

A re-investigation of the reaction showed, in accordance with VotoCek s hypothesis, that the compounds obtained have properties (for example, color reactions, ultraviolet and infrared spectra, hydrolysis when examined chromatographically) similar to those of the /3-(glycosylamino) a, 8-un-saturated esters or ketones prepared directly from glycosylamines and i3-dicarbonyl compounds. The derivatives from L-rhamnose and ammonia with ethyl acetoacetate and with 2,4-pentanedione are, indeed, identical... 

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