Enzymatic condensation of dopamine and secologanin by cell-free extracts of Alangium lamarckii

Two novel enzyme activities involved in the condensation of dopamine and secologanin were discovered in the cell-free extracts prepared from the leaves of Alangium lamarckii. The extracts condensed dopamine and secologanin rapidly at pH 7.5 to form both (1R)-deacetylipecoside (1) and (1S)- deacetylisoipecoside (2) which were converted spontaneously to demethylalangiside (3) and demethylisoalangiside (4), respectively. Identification of the enzymatic reaction products was performed by using TLC, HPLC-photodiode array detector and LC-MS. A simple enzyme assay by a spectrophotometric method was developed for enzyme activity detection during enzyme purification. The discovery of these two enzyme activities in A. lamarckii suggested that the naturally occurring (S)- and (R)-forms of various tetrahydroisoquinoline-monoterpene alkaloids and nitrogenous glucosides found in this plant are determined by the first enzymatic step of dopamine and secologanin condensation which yields either the (1R) or the (1S)-condensation product.