Structure-Based Design and Synthesis of New Estrane-Pyridine Derivatives as Cytochrome P450 (CYP) 1B1 Inhibitors

Abstract

Inhibition of cytochrome P450 (CYP) 1B1 is a promising therapeutic strategy, as such an inhibitor could modulate the bioactivation of procarcinogens while reducing drug resistance. Based on docking studies, the synthesis of 12 estra-1,3,5(10)-triene derivatives containing a pyridin-3-/4-yl moiety at position C2, C3, or C4 was performed, and we measured their inhibitory activity on CYP1B1 using the ethoxyresorufin-O-deethylase (EROD) assay. The position of the nitrogen atom in the aromatic ring has little influence on their inhibition potency, but compounds with a pyridinyl at C2 of the steroid nucleus are more potent CYP1B1 inhibitors than those with a pyridinyl at C3 or C4. Estradiol derivatives (OH at C17β) are also 10-fold more potent inhibitors than estrone derivatives (carbonyl at C17). Thus, 2-(pyridin-3-yl)-estradiol (4a) is the best CYP1B1 inhibitor (IC₅₀ = 0.011 μM) from this series of compounds, and the best steroid inhibitor reported until now. It is also 7.5-fold more potent than the well-known nonsteroidal CYP1B1 inhibitor α-naphthoflavone (IC₅₀ = 0.083 μM).

Figure 1

Conversion of estrogenic C18-steroid hormones by CYP1B1 (A) and the structures of the newly synthesized CYP1B1 inhibitors (B). Partial numbering of carbons (left structure) and steroid (A–D) ring identification (right structure) are reported.

Figure 2

Binding mode of 3a (A), 6a (B), 11a (C), and 4a (D) docked in CYP1B1. Black sticks represent the heme group, whereas the iron atom is highlighted as a red sphere. Images were produced using the UCSF Chimera package.

Scheme 1

Reagents and conditions: (a) Hg(OAc)₂, I₂, AcOH, THF, rt, 2 h; (b) MOM-Cl, Cs₂CO₃, ACN, reflux, 2–3 h; (c) 3- or 4-pyridine boronic acid, Pd(dppf)Cl₂, K₃PO₄, DMF, MW, 120 °C, 2–3 h; (d) 10% HCl aq. in MeOH (1:9), 50 °C, overnight; (e) NaBH₄, MeOH/DCM (9:1), 0 °C, 2–3 h.

Scheme 2

Reagents and conditions: (a) Tf₂O, 2,6-lutidine, DMAP, DCM, 0 °C to rt; (b) 3- or 4-pyridine boronic acid, Pd(dppf)Cl₂, K₃PO₄, DMF, MW, 120 °C, 2–3 h; (c) NaBH₄, MeOH/DCM (9:1), 0 °C, 2–3 h.

Scheme 3

Reagents and conditions: (a) Br₂, 80% aq. acetic acid, Fe, 20 °C; (b) MOM-Cl, Cs₂CO₃, ACN, reflux, 2–3 h; (c) 3- or 4-pyridine boronic acid, Pd(PPh₃)₄, toluene, EtOH, K₂CO₃ aq. (2 M), reflux, overnight; (d) 10% HCl aq. in MeOH (1:9), 50 °C, overnight; (e) NaBH₄, MeOH/DCM (9:1), 0 °C, 2–3 h.

Figure 3

Plasmatic concentrations of 2-(pyridin-3-yl)-E2 (4a) and 2-(pyridin-3-yl)-E1 (3a) after a sc injection of 4a (0.66 mg in 500 μL of PG/DMSO (92:8); 2.0 mg/kg) in rats. AUC: area under curve.