Synthesis and properties of amino acid-based polyacetylenes

The present study deals with the synthesis and polymerization of novel amino acid-derived acetylene monomers, N-(tert-butoxycarbonyl)-L-alanine N'-propargylamide (L-1A), N-(tert-butoxycarbonyl)-L-alanine N-methyl-N'-propargylamide (N-Me-L-1A), and N-(tert-butoxycarbonyl)-L-alanine propargyl ester (L-1E) and the analysis of the properties of the formed polymers. The monomers were synthesized by the condensation of N-(tert-butoxycarbonyl)-L-alanine with propargylamine, N-methylpropargylamine, and propargyl alcohol in 50, 89, and 72% yields, respectively. They satisfactorily underwent polymerization with (nbd)Rh+[eta(6)-C6H5B-(C6H5)(3)] as a catalyst ([M](0)/[Cat] = 10-200) in THF and CH2O2 at 0-50 degreesC to afford the corresponding polymers with M-n's in the range 1 x 10(4)-2 x 10(5). Poly(L-1A) exhibited a large specific rotation {[alpha]D = -1349degrees (CH2Cl2)} and a CD signal [theta](max) = -3.2 x 10(4) deg cm(2) dmol(-1) (CHCl3), suggesting that it takes a helical conformation. On the other hand, poly(N-Me-1A) and poly(L-1E) showed no evidence of a helical structure. The helical structure of poly(L-1A) was deformed by the addition of MeOH.