Forty-eight derivatives of phorbol (9) and isophorbol (14) were evaluated for their inhibition of human immunodeficiency virus (HIV)-1 induced cytopathic effects (CPE) on MT-4 cells, as well as their activation of protein kinase C (PKC), as indices of anti-HIV-1 and tumor promoting activities, respectively. Of these compounds, the most potent inhibition of CPE was observed in 12-
O-tetradecanoylphorbol 13-acetate (8) and 12-
O-acetylphorbol 13-decanoate (6). The former also showed the strongest PKC activation activity, while the latter showed no activity at 10 ng/ml. Both activities were generally observed in those phorbol derivatives with an A/B
trans configuration, but not in the isophorbol derivatives with an A/B
cis configuration. Acetylation of 20-OH in the phorbol derivatives significantly reduced the inhibition of CPE, as shown in 12-
O-, 20-
O-diacetylphorbol 13-decanoate (6a) (IC
100=15.6 μg/ml)
vs. compound 6 (IC
100=0.0076 μg/ml), and 12-
O-tetradecanoylphorbol 13,20-diacetate (8a) (IC
100=15.6 μg/ml)
vs. 12-
O-tetradecanoylphorbol 13-acetate (8) (IC
100=0.00048 μg/ml), except in the case of 12-
O-decanoylphorbol 13-(2-methylbutyrate) (4) and phorbol 12,13-diacetate (9c). The reduction of a carbonyl group at C-3 abruptly reduced the inhibition of CPE, as observed in 3β-hydroxyphorbol 12,13,20-triacetate (9f) (IC
100=500 μg/ml)
vs. phorbol 12,13,20-triacetate (9d) (IC
100=62.5 μg/ml). Although 8 was equipotent in the inhibition of CPE, and activation of PKC, both activities were abruptly decreased by the acetylation of 20-OH and methylation of 4-OH [as in 8a and 4-
O-methyl-12-
O-tetradecanoylphorbol 13,20-diacetate (8b), respectively]. On the other hand, its positional isomer (12-
O-acetylphorbol 13-tetradecanoate (8c) showed neither activities. The removal of a long acyl group in 8 led to a substantial loss of both activities, as shown in phorbol 13-acetate (9b). Of the 12-
O-acetyl-13-
O-acylphorbol derivatives, the highest inhibition of CPE was observed in 6, which has a dodecanoyl residue at C-13. Both an increase and decrease in the number of fatty acid carbon chains resulted in significant reduction of the inhibition of CPE.
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