Straightforward synthesis of derivatives of d- and l-galactonic acids as precursors of stereoregular polymers

✍ Scribed by Carmen L. Romero Zaliz; Oscar Varela

• Publisher: Elsevier Science
• Year: 2003
• Tongue: English
• Weight: 230 KB
• Volume: 14
• Category: Article
• ISSN: 0957-4166
• DOI: 10.1016/s0957-4166(03)00588-3

✦ Synopsis

High yielding routes for the synthesis of selectively protected derivatives of D-and L-galactonic acids, having free OH or NH 2 groups at the C-6 position, are reported. The successful direct per-O-methylation of galactonic acid derivatives from the corresponding galactono-1,4-lactones was developed as a key step of the sequence. For example, 6-azido-6-deoxy-L-galactono-1,4lactone 16 was converted into the potassium salt and methylated (NaH, DMSO, MeI) to the methyl ester of the 2,3,4,5-tetra-Omethyl derivative 12. Compound 16 was readily prepared by bromination at C-6 of L-galactonolactone 1 and isopropylidenation; followed by substitution of bromine by azide and removal of the protecting groups. Hydrolysis of the methyl ester of 12 and hydrogenation of the azide led to the tetra-O-methyl derivative of the 6-amino acid 18 with 52% overall yield from 1. The same sequence applied to D-galactonolactone 19 led to the enantiomeric amino acid 25 with a 47% overall yield.