Reversal of Multidrug Resistance by Tropane Alkaloids from the Stems of Erythroxylum rotundifolium

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Abstract
Six tropane alkaloid esters were isolated from the stems of Erythroxylum rotundifolium. The structures of three new tropane esters, 7β-hydroxy-6β-(3,4,5-trimethoxybenzoyloxy)-3α-(E)-(3,4,5-trimethoxycinnamoyloxy)tropane (1), 6β-benzoyloxy-3α-(Z)-(3,4,5-trimethoxycinnamoyloxy)tropane (2), and (−)-6β-benzoyloxy-3α-hydroxytropane (3), were established by spectroscopic techniques. When alkaloids 1−6 were evaluated against a panel of human cancer cell lines, the new compound 6β-benzoyloxy-3α-(Z)-(3,4,5-trimethoxycinnamoyloxy)tropane (2) and three known compounds, 6β-benzoyloxy-3α-(3,4,5-trimethoxycinnamoyloxy)tropane (4), 6β-benzoyloxy-3α-(E)-(3,4,5-trimethoxycinnamoyloxy)tropane-7β-ol (5), and 7β-acetoxy-6β-benzoyloxy-3α-(E)-(3,4,5-trimethoxycinnamoyloxy)tropane (6), demonstrated greatest activity with multidrug-resistant oral epidermoid carcinoma (KB-V1) cells incubated in the presence of vinblastine. Thus, tropane esters of this type can reverse the multidrug-resistance phenotype, presumably by interacting with P-glycoprotein.

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