Highly increased cellular accumulation of vincristine, a useful hydrophobic antitumor-drug, in multidrug-resistant solid cancer cells induced by a simply reduced taxinine

Regio- and/or chemo-selective reductions of taxinine (1a), a taxane diterpenoid readily obtainable from the needles of a Japanese yew (Taxus cuspidata), at the 5-O-cinnamoyl and 4-exo-methylene moieties have been accomplished by the catalytic hydrogenation over Pd/C or Rh/C to obtain 5-O-phenylpropionylated taxinine A (1b), 5-O-cyclohexylpropionylated taxinine A (1c), and 5-O-phenylpropionylated 4,20-dihydrotaxinine A (2a) in almost quantitative yields, respectively. Among them, taxoid 1b was found to be highly effective in increasing the cellular accumulation of vincristine in the multidrug-resistant human ovarian cancer cells compared with the cases of verapamil and the previously reported taxoids.