Straightforward synthesis of derivatives of D- and L-galactonic acids as precursors of stereoregular polymers
High yielding routes for the synthesis of selectively protected derivatives of D- and L-galactonic acids, having free OH or NH2 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...
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| Autores principales: | , |
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| Formato: | JOUR |
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| Acceso en línea: | http://hdl.handle.net/20.500.12110/paper_09574166_v14_n17_p2579_RomeroZaliz |
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| Sumario: | High yielding routes for the synthesis of selectively protected derivatives of D- and L-galactonic acids, having free OH or NH2 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-1,4-lactone 16 was converted into the potassium salt and methylated (NaH, DMSO, MeI) to the methyl ester of the 2,3,4,5-tetra-O-methyl 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. © 2003 Elsevier Ltd. All rights reserved. |
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