A tetrameric dialdehyde formed in the reaction of butyral dehyde and benzylamine: A possible intermediary component for protein cross‐linking induced by lipid oxidation

We investigated the reaction of butyraldehyde and benzylamine and analyzed the products to identify the components that produce protein cross‐linking in the reaction of butyraldehyde and proteins. When the mixtures of butyraldehyde and benzylamine were incubated at pH 7 and 37°C for 48 hr, many reaction products other than 2‐ethyl‐2‐hexenal and Schiff bases of butyraldehyde and 2‐ethyl‐2‐hexenal were produced. Fluorescent substance(s) were formed only in the presence of dissolved oxygen in the reaction mixture. Three new nonflourescent products— d,e and f —were isolated, and their structures are suggested to be 2,9‐dibenzyl‐4,6,8‐triethyl‐7‐propyl‐2,9‐diazabicyclo[3,3,1] nona‐3‐ene ( d ), 1‐phenyl‐2‐benzyl‐ 4,5,7‐triethyl‐6‐propyl‐1H,2H,3H,5H,6H,7H,8H‐pyrido[1,2‐clpyrimidine ( e ) and 1‐phenyl‐2‐benzyl‐4,5,7‐triethyl‐6‐propyl‐1H,2H,4aH,5H,6H,7H,8H‐pyrido[1,2‐ c ]pyrimidine ( f ). Formation of these compounds suggested that the protein, cross‐linking with butyraldehyde is caused by the tretrameric dialdehyde formed by repeated aldol condensation and Michael reaction of butyraldehyde.