Synthesis and Photophysical Properties of Charge-Transfer-Based Pyrimidine-Derived a-Amino Acids

The four-step synthesis of fluorescent pyrimidine-derived a-amino acids from an L-aspartic acid derivative is described. The key synthetic steps involved preparation of ynone intermediates via the reaction of alkynyl lithium salts with a Weinreb amide, followed by an ytterbium-catalyzed heterocycliza-tion reaction with amidines. Variation of substituents at the C2-and C4-position of the pyrimidine ring allowed tuning of the photoluminescent properties of the a-amino acids. This revealed that a combination of highly conjugated or electron-rich aryl substituents with the p-deficient pyrimidine motif resulted in fluorophores with the highest quantum yields and overall brightness. Further analysis of the most fluorogenic a-amino acid demonstrated solvatochromism and sensitivity to pH.

Automated summary

This paper describes a four-step synthesis of fluorescent pyrimidine-derived α-amino acids from an L-aspartic acid derivative. The key synthetic steps involved the preparation of ynone intermediates through the reaction of alkynyl lithium salts with a Weinreb amide, followed by a heterocyclization reaction with amidines catalyzed by ytterbium. The substitution of the C2 and C4 positions of the pyrimidine ring allowed tuning of the photoluminescent properties of the α-amino acids. The study also revealed that fluorophores with the highest quantum yields and overall brightness were obtained by combining highly conjugated or electron-rich aryl substituents with the p-deficient pyrimidine motif. Further analysis demonstrated solvatochromism and sensitivity to pH in the most fluorogenic α-amino acid.