Glycosylamines anomers

A test of this hypothesis would lie in studying the products of the reaction of a 2-deoxy analog of LXX with LXVII, LXXI, or LXXIV, in order to ascertain whether the a and /3 anomers of the nucleoside would be formed. Such a 2-deoxyglycosylamine derivative has not yet been synthesized for the present, this effectively precludes the use of the glycosylamine reaction for the synthesis of 2-deoxypentonucleosides. 

Benzoylation thus resembles acetylation in that the glycosylamine reacts in the pyranose form. However, only one anomer of each benzoate has been isolated. Again, this is an attractive method, alternative to the use of 0-benzoylaldosyl bromides, for preparing aldose benzoates with Cl unsubstituted. 

Glycosylamines (NH2 on Cl) are configurationally unstable, but it is possible to measure the of the mixture and the difference between a- and (3-anomers by the technique described by eqn (2.8). The marginally stronger basicity of equatorial glycosylamines is attributed to the more ready solvation of their conjugate acids, but the anomeric effect makes the difference smaller than in carbocyclic systems. 

Carboxy-activated amlnoaclds have been coupled with unprotected glycosylamines to prepare both anomers of N-(L-3-aspartoyl)-D-... 

Glycosylamines, in particular the O-pivaloyl protected galactopyranosylamine 15 proved to be very efficient chiral templates in asymmetric Strecker (28) and Ugi syntheses (29) of a-amino acid derivatives. In both these processes the imines 16 formed from the galactosylamine 15 and aldehydes are the real chiral substrates. The N-galactosyl imines 16 of aromatic aldehydes can be synthesized from 15 and the aldehyde in n-pentane in the presence of molecular sieves (4A) and dried silica gel. Under these conditions anomerization of the imines can be prevented. The compounds 16 are isolated in crystalline form and contain less than 4% of the corresponding a-anomer. 

Tri- and tetra-peptide analogues incorporating an a-atnino acid at the anomeric position, e.g. 33, were synthesized by way of a novel oxidative ting contraction of 2-amino-2-deoxy-heptonic acid derivative 31 to give heptulosonic acid glycosylamine 32 and its anomer (Scheme 6). The spirocyclic diketopiperazine 35 was obtained from 34 it could be 0-deprotected under acidic conditions then anomerized to the thermodynamically favoured C-2 q>imer with strong base. See also reference 3 for a general route to anomeric a-amino acids. 

The conformations of the o- and /3-anomers of 2,3,4-tri-Q-acetyl-D-arabinopyranosyl azide have been predicted from semi-empirical quantum chemical calculations. Neutral Raney nickel has been used to convert a glycosyl azide to the corresponding glycosylamine in the presence of Q-benzyl protecting groups. " CHaOSi. ... 

The aminoimidazole nucleoside derivative (138) has been shown to undergo rearrangement in aqueous buffer at pH7 to give the glycosylamines (139), with the p-anomer predominating this observation may well be relevant to the previously-noted lability of the corresponding nucleoside and... 

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