Synthesis of 1, 2, 3, 4-Tetrahydro-β-carboline Derivatives as Hepatoprotective Agents. IV. Positional Isomers of 1, 2, 3, 4-Tetrahydro-2-methylthiothiocarbonyl-β-carboline-3-carboxylic Acid and Its 1-Alkylated Derivatives

Two tetrahydro-β-carboline-1-and-4-carboxylic acids (1b, c) and the corresponding hydroxymethyl derivatives (2b, c), which are positional isomers of the 3-carboxylic acid (1a) and its 3-hydroxymethyl derivative (2a), were synthesized and tested for hepatoprotective activity against carbon tetrachloride (CCl4) -induced liver damage in mice. The hepatoprotective activity of these positional isomers decreased in the following order;1a> 1b> 1c> and 2a > 2b>2c. The effect of alkyl substitution at the 1 position of 1a and 2a was also examined with the cis and trans isomers (5a, b-14a, b). Compounds with small alkyl groups such as Me and Et showed potent activity. Lengthening of the alkyl group generally caused a decrease in activity. In a series of the stereoisomers of the 3-carboxylic acids (5a, b-9a, b), the cis isomers tend to be more active than the trans counterparts.