Selective hydroboration of dieneamines. Formation of hydroxyalkylphenothiazines as MDR modulators

N-dienylphenothiazines synthesized from tetrazolo[1,5-a]pyridinium salts by treatment with phenothiazine were subjected to catalytic hydrogenation to yield N-butylphenothiazines, whereas transformation of these dienes with borane dimethyl sulfide (BH3 × Me2S) resulted in selective hydroboration of one double bond and full reduction of the other double bond to give 2-hydroxybutylphenothiazines. Position of the hydroxyl group was supported by NMR spectroscopy and verified by X-ray analysis. Comparison of MDR modulatory activity of the new derivatives revealed that the hydroxybutyl compounds are promising candidates for development of novel MDR inhibitors.

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