Studies on 1, 2, 3, 4-Tetrahydroisoquinolines. III. Syntheses and β-Adrenoceptor Activities of Methyl Derivatives of Trimetoquinol

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Three methyl derivatives (S-2, S-3, and S-4) of trimetoquinol (TMQ), in which one or both of the ring positions ortho to a phenolic group are substituted by a methyl group, were synthesized and evaluated for bronchodilating activity. They were prepared by NaBH₃CN reduction of the Mannich bases (S-6, S-8, and S-23) via the quaternary salts in a one-pot procedure followed by catalytic reduction on 10% Pd-C. A comparison of the 5-methyl derivative (S-2) with TMQ revealed that the duration of bronchodilating effect of S-2 is considerably longer than that of TMQ on intraduodenal administration.