Synthesis and polymerization of conveniently substituted 6-amino-6-deoxy-D-galactonic acid derivatives

Abstract

Methyl 6-azido-6-deoxy-2,3:4,5-di-O-isopropylidene-D-galactonate (1), prepared in two steps from D-galactono-1,4-lactone, was hydrolyzed to the corresponding acid 2, which was esterified with phenol (PhOH) in the presence of dicyclohexylcarbodiimide (DCC) to give the phenyl ester 3. Hydrogenolysis of the azide function of 3 yielded the hydrochloride derivative of the amino acid 4. Compound 4 is conveniently substituted for the polycondensation; therefore, this reaction was conducted using DMF as solvent and N,N-diisopropylethylamine as a basic catalyst. The MALDI-TOF mass spectrum of the isolated product (5) indicated that this was a mixture of the cyclic trimer (M + Na+, 793.7) and linear oligomers (from the tetramer to the tetradecamer). To favor the linear polymerization the dimeric amino acid 10 was prepared starting from 2. Thus, hydrogenation of 2 gave the amino acid 6, and treatment of 2 with pentachlorophenol-DCC gave the pentachlorophenyl ester 7. Coupling of 6 with 7 in the presence of DCC gave the dimer 8, which was converted (PhOH, DCC) into 9. Hydrogenolysis of 9 afforded the dimeric amino acid 10, which was polymerized under the conditions employed for 4. The resulting polyamide 11 was highly soluble in common organic solvents, and its molecular weight was established by MALDI-TOF MS and size exclusion chromatography (Mw = 2700). ©ARKAT.