Sustainable phosphate-catalyzed synthesis of non-symmetric pyrazines in water – mechanistic insights, biocatalytic applications and industrial potential

Abstract

Pyrazines are pivotal flavor compounds with widespread applications in the food, pharmaceutical, and chemical industries. Their natural abundance is low, and traditional synthetic methods often involve hazardous conditions unsuitable for the food sector. In this study, we present a novel biocatalytic methodology for synthesising non-symmetric trisubstituted pyrazines using aminoacetone dimerisation followed by electrophile incorporation under environmentally benign conditions, catalyzed by phosphate anion. The approach includes the employment of l-threonine dehydrogenase from Cupriavidus necator to generate aminoacetone in situ from natural l-threonine, integrating biocatalysis with green chemistry principles. Detailed mechanistic investigations, supported by control experiments and DFT calculations, revealed the critical role of phosphate buffering, an E1cB elimination, and a tautomerisation-driven pathway for product formation. The methodology demonstrates broad substrate scope and scalability, yielding pyrazines with diverse structural modifications up to 96% yields. This work establishes a starting point for the industrial production of non-symmetric pyrazines, addressing current regulatory and environmental demands in the flavor and fragrance sector.