Synthesis of regioisomeric,stereoregular AABB-type polyamides from chiral diamines and diacids derived from natural amino acids

Two regioisomeric and stereoregular AABB-type polyamides have been synthesized using l-glutamic acid 1 and l-alaninol 4 as sources of chirality. From 4, two derivatives of chiral diamines were prepared and regioselectively condensed with pentachlorophenyl 5-oxo-(S)-2-tetrahydrofurancarboxylate 3, derived from 1. Manipulation of functional groups and convenient deprotections led to the ammonium salts of N-1′-amino-(S)-2′-propyl]- and N-(S)-2′-amino-1′-propyl]-5-oxo-(S)-2-tetrahydrofurancarboxyamide 11 and 15, respectively, in which the building blocks derived from 1 and 4 are linked through an amido group. Compounds 11 and 15 are, in fact, α,ω-amino acids having amino and lactone groups, and hence activated for polycondensation. Thus, polymerization of 11 took place under regio- and stereo-control to afford stereoregular polyN-(1′-amino-(S)-2′-propyl)-carboxyamido-(S)-2-hydroxypentan-5-oic acid] (16). Similar polycondensation of 15, under the optimized conditions employed for the synthesis of 16, gave the regioisomeric polyamide 17, which exhibited a molecular weight lower than that of 16. The thermal and spectroscopic properties of optically active AABB-polyamides 16 and 17 are described.