Abstract
AbstractH‐D,L‐Ala‐D,L‐Ala‐OH (3) synthesized from Boc‐D,L‐Ala‐OH and H‐D,L‐Ala‐OMe by means of ethyl 2‐ethoxy‐1,2‐dihydroquinoline‐1‐carboxylate was shown by 15N NMR spectroscopy to be a mixture of the L‐L and D‐D enantiomers. Using this racemic mixture N‐(6‐isothiocyanatohexanoyl)‐D,L‐Ala‐D,L‐Ala‐OH (1a) was synthesized and then polymerized in N,N′‐dimethylformamide at 120°C. The 15N NMR and 13C NMR spectra of the resulting polymer (ε‐Aca‐D,L‐Ala‐D,L‐Ala)n (2) demonstrate that the polymerization involved to a large extent racemization. The 15N NMR spectra taken in various solvents turned out to be ca. 5 times more sensitive to stereoisomerism than 13C NMR spectra. The solvents were found to have a strong influence on the chemical shift and on the line width.
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