17α-Alkan (or alkyn) amide derivatives of estradiol as inhibitors of steroid-sulfatase activity

To develop inhibitors of steroid sulfatase without residual estrogenic activity, we have designed a series of estradiol (E-2) derivatives bearing an alkan (or alkyn) amide side chain at position 17 alpha. A hydrophobic alkyl group was selected from our previous study where 17 alpha-octyl-E-2 was found to inhibit strongly the steroid-sulfatase activity. Furthermore, it is known that an alkylamide side chain blocks the estrogen-receptor activation. Starting from ethynylestradiol, the chemical synthesis of target compounds was short and efficient with overall yields of 22-42% (3 or 4 steps). Among these compounds, N-octyl,N-methyl-3-(3',17' beta-dihydroxy-1',3',5'(10')-estratrien-17' alpha-yl)-propanamide (15) was the most potent inhibitor, with an IC50 value of 0.08 mu M for the transformation of estrone sulfate (E1S) to estrone (E-1) by homogenated JEG-3 cells. N-butyl, N-hexyl, and N,N-dioctyl propanamide derivatives of E-2 (IC50 values of 6.4, 2.8, and >20 mu M, respectively) were less potent inhibitors than N-octyl analog 15. Furthermore, the unsaturated propynamide analog of 15 gave lower inhibition (four times) than the saturated compound. Compound 15 is also about 100-fold more effective in interacting with the enzyme than substrate E1S itself. The ability of target compounds to bind the estrogen receptor, to stimulate the proliferation of estrogen-sensitive ZR-75-1 cells, or to inhibit the E-2-stimulation of ZR-75-1 cells was also evaluated. Although a mixed estrogenic/anti-estrogenic activity was obtained for tested compounds at 1 mu M, no estrogenic activity was observed at 0.03 mu M for 15. In conclusion, a promising inhibitor of steroid-sulfatase activity was obtained by introducing a hydrophobic octyl group in a 17 alpha-propanamide side chain of E-2, but further structure-activity relationships (SAR) studies are necessary to minimize the residual estrogenic activity. (C) 1999 Elsevier Science Inc. All rights reserved.