Non-enzymic coupling of vindoline and catharanthine to synthesize the dihydropyridinium intermediate (DHPI) of dimeric alkaloids was achieved under near-ultraviolet light irradiation with a peak at 370 nm in the presence of flavin mononucleotide (FMN). Circular dichroism analysis showed that 3’,4’-andydrovinblastine (AVLB), a reduced product of DHPI, had an alpha-configuration at the C-18’ chiral center, like natural dimeric alkaloids. The amount of AVLB was about 50% of the initial amount of vindoline under the conditions optimized in the study, namely irradiation with 20 W/m(2) near-ultraviolet light in the presence of 50 mu M FMN and 1 mM manganous ion at pH 7 and 25 degrees C. These results suggest that this non-enzymic coupling system can supply natural DHPI in sufficient amounts under biomimetic conditions and that it is suitable for investigating subsequent one-pot biosynthetic reactions; for example, to detect the enzyme mediating vinblastine synthesis from DHPI.