Theoretical investigation of the relationship between four-carbon d-sugars and five l-amino acids

This study constructed the relationship between l-amino acids and four-carbon d-sugar using quantum theory. Theoretically, an l-amino acid could react with the ketone to afford the corresponding Schiff base which may take place an Aldol reaction with a molecule of formaldehyde. An assumption is proposed that the Aldol addition products with (R) or (S) configuration could have different quantity due to the effect from stereogenic center of l-amino acid. By hydrolysis of the Aldol addition, different d- or l-sugar would form. Thus, B3LYP, WP1MPW91 and wB97XD theories were used for the energy difference computations at the 6-311++G(2d,p) level in the gas phase, or in water using PCM and SMD model, respectively. The predicted ee value sequence agrees well to the experimental result in the asymmetric synthesis of 3-carbon sugar using five l-amino acids. Further theoretical study exhibited that 4-carbon D sugar should form if the corresponding l-amino acid is used. The ee values of the 4-carbon sugar are bigger than those of 3-carbon d-sugars catalyzed by the same l-amino acids. This looks like the chiral amplification in the procedure.