PubMed · 15412787
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1950. GALACTOSE utilization.. https://doi.org/10.1111/j.1753-4887.1950.tb02385.x
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A short and high-yielding synthesis has been devised to prepare C-linked 2-deoxy-2-acetamido-alpha-D-galactopyranose derivative 3. One of the main advantages of this approach is that it employs commercially available and inexpensive d-glucosamine as the starting material. The key steps include a highly stereoselective C-allylation followed by epimerization of the C-4 hydroxyl group. Building block 3 and orthogonally protected C-linked 2-deoxy-2-acetamido-alpha-D-galactopyranose derivative 2 were obtained in 44% overall yield (six steps) and 29% overall yield (eight steps), respectively. This represents a significant improvement over previously reported syntheses.
Competitive glycosylation experiments with a galactofuranosyl trichloroacetimidate donor were performed with glucosamine acceptors having a free 4-OH group and carrying different protecting groups at N-2, O-3, and O-6. The most reactive acceptor is the N-dimethylmaleimido 3,6-di-O-benzylated derivative (6c), which reacts even faster than the oxazolidinone 1a. Molecular orbital calculations have helped to rationalize these experimental facts in terms of a hard-hard reaction occurring between the donor and the acceptor.
Schemes to include a treatment of torsional anharmonicity in the conformational analysis of biological molecules are introduced. The approaches combine ab initio electronic energies and harmonic frequencies with anharmonic torsional partition functions calculated using the torsional path integral Monte Carlo method on affordable potential energy surfaces. The schemes are applied to the conformational study of the monosaccharide beta-d-galactose in the gas phase. The global minimum structure is almost exclusively populated at 100 K, but a large number of conformers are present at ambient and higher temperatures. Both quantum mechanical and anharmonic effects in the torsional modes have little effect on the populations at all temperatures considered, and it is, therefore, expected that standard harmonic treatments are satisfactory for the conformational study of monosaccharides.