Novel 13α-estrone derivatives were synthesized by Sonogashira coupling. Transformations of 2- or 4-iodo regioisomers of 13α-estrone and its 3-methyl ether were carried out under different conditions in a microwave reactor. The 2-iodo isomers were reacted with para-substituted phenylacetylenes using Pd(PPh3)4 as catalyst and CuI as a cocatalyst. Coupling reactions of 4-iodo derivatives could be achieved by changing the catalyst to Pd(PPh3)2Cl2. The product phenethynyl derivatives were partially or fully saturated. Compounds bearing a phenolic OH group furnished benzofurans under the conditions used for the partial saturation. The inhibitory effects of the compounds on human placental 17β-hydroxysteroid dehydrogenase type 1 isozyme (17β-HSD1) were investigated by an in vitro radiosubstrate incubation method. Certain 3-hydroxy-2-phenethynyl or -phenethyl derivatives proved to be potent 17β-HSD1 inhibitors, displaying submicromolar IC50 values.

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Ring A halogenated 13α-, 13β-, and 17-deoxy-13α-estrone derivatives were synthesised with N-halosuccinimides as electrophile triggers. Substitutions occurred at positions C-2 and/or C-4. The potential inhibitory action of the halogenated estrones on human aromatase, steroid sulfatase, or 17β-hydroxysteroid dehydrogenase 1 activity was investigated via in vitro radiosubstrate incubation. Potent submicromolar or low micromolar inhibitors were identified with occasional dual or multiple inhibitory properties. Valuable structure–activity relationships were established from the comparison of the inhibitory data obtained. Kinetic experiments performed with selected compounds revealed competitive reversible inhibition mechanisms against 17β-hydroxysteroid dehydrogenase 1 and competitive irreversible manner in the inhibition of the steroid sulfatase enzyme.

The inhibitory effects of 13-epimeric estrones, D-secooxime and D-secoalcohol estrone compounds on human placental 17b-hydroxysteroid dehydrogenase type 1 isozyme (17b-HSD1) were investigated. The transformation of estrone to 17b-estradiol was studied by an in vitro radiosubstrate incubation method. 13a-Estrone inhibited the enzyme activity effectively with an IC 50 value of 1.2 mM, which indicates that enzyme affinity is similar to that of the natural estrone substrate. The 13b derivatives and the compounds bearing a 3-hydroxy group generally exerted stronger inhibition than the 13a and 3-ether counterparts. The 3-hydroxy13b-D-secoalcohol and the 3-hydroxy-13a-D-secooxime displayed an outstanding cofactor dependence, i.e. more efficient inhibition in the presence of NADH than NADPH. The 3-hydroxy13b-D-secooxime has an IC 50 value of 0.070 mM and is one of the most effective 17b-HSD1 inhibitors reported to date in the literature.