Synthesis of (2R,3S,4R)-3,4-dihydroxyproline from D-ribonolactone; an approach to the synthesis of polyfunctionalised D-amino acids from sugar lactones. X-Ray molecular structures of 2-azido-3,4-O-(R)-benzylidene-2-deoxy-D-ribono-1,5-lactone, 2-azido-2-deoxy-D-ribono-1,4-lactone, and (2R,3S,3R)-3,4-dihydroxyproline

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Abstract
A general approach to the synthesis of polyfunctionalised amino acids from sugar lactones, in which nucleophilic displacement by azide ion of O-trifluoromethanesulphonyl esters adjacent to the lactone carbonyl is the key step, is discussed and is exemplified by the synthesis of the D-amino acid (2R,3S,4R)-3,4-dihydroxyproline from D-ribonolactone; unexpectedly, displacement of a triflate by azide in the C-2 position of ribonolactone occurs with retention of configuration. The X-ray crystal structures of 2-azido-3,4-O-(R)-benzylidene-2-deoxy-D-ribono-1,5-lactone, 2-azido-2-deoxy-D-ribono-1,4-lactone, and (2R,3S,4R)-3,4-dihydroxyproline are reported. I.r. spectroscopy does not discriminate reliably between 1,4-and 1,5-lactones, and X-ray crystallography is necessary to provide reliable structural information in this area.