O-methylation of dopamine-o-sulfates with catechol-0-methyltransferase

[2H2]-dopamine-3-0-sulfate (DM-3-0-S) and [2H2]-dopamine-4-0-sulfate (DM-4-0-S) were synthesized to investigate the possibility of their being substrates for catechol-0-methyltransferase (COMT). [2H5]-3-0-methyldopamine (3-0-Me-DM) and [2H5]-4-0-methyldopamine (4-0-Me-DM) were also synthesized as internal standards for the determination of enzymatic products by gas chromatography-mass spectrometry (GC-MS). [2H2]-DM-3-0-S or [2H2]-DM-4-0-S was incubated at 37 degrees for 60 min in the presence of S-adenosyl-L-methionine with a crude enzyme preparation obtained from rat liver homogenate. The incubation mixture was treated with 0.5N HCl at 100 degrees C for 1h to hydrolyze the remaining sulfate moiety. The reaction products were extracted with an Amberlite XAD-4, derivatized with pentafluoropropionic anhydride and determined by GC-MS. When [2H2]-DM-3-0-S was used as a substrate, [2H2]-3-0-Me-DM was found to be a major product accompanied by [2H2]-4-0-Me-DM as a minor product. The ratio of [2H2]-3-0-Me-DM to [2H2]-4-0-Me-DM was found to be 26:1, while the ratio was 5.4:1 when [2H2]-dopamine was used as a substrate. When [2H2]-DM-4-0-S served as a substrate, [2H2]-3-0-Me-DM was preferentially produced without detectable formation of [2H2]-4-0-Me-DM.