The carboxylation activity of vitamin K analogs with substitutions at position 2, 3, or 5.

While menadione plus NADH or menadiol is unable to promote in vitro vitamin K-dependent carboxylation in a solubilized rat liver microsomal incubation system (as does vitamin K1 hydroquinone or vitamin K1 plus NADH), addition of various monoand dithiols with the menadione produces activity. Adducts of menadione and a number of thiols have been prepared in pure form and were found to be able to replace vitamin K1 in the in vitro carboxylation reaction. It appears that the thioether side chain added must be uncharged (carboxy1 or amino groups, or both, in this side chain result in compounds which are inactive) but may be either hydrophobic (e.g. thiobutane) or hydrophilic (e.g. thiopropanediol). The most active adducts appear to be those of the dithiol compounds (e.g. dithiothreitol, dithioerythritol, dithiobutane). The side chain attached to the sulfur may be aliphatic or aromatic and as short as a single methyl. These data indicate noninvolvement of the vitamin K polyisoprene side chain in the reaction and contribute information regarding structural requirements for the carboxylation system. In addition to 34hioethers of menadione, 3-O-ethers and the non-isoprenoid compound, 3-pentadecyl menadione, all are active in carboxylation. Substitution in position 5 by a hydroxyl or alkoxy eliminates carboxylation activity, as does replacement of the a-methyl group by hydroxy or methoxy groups.