Benzothiepin-derived molecular scaffolds for estrogen receptor modulators: synthesis and antagonistic effects in breast cancer cells

Figures & data

Figure 1 Structure of estradiol and SERMs.

Scheme 1 Synthesis of Benzothiepins 13a–c and 14. Scheme reagents: (a) R = H, F; PPA, 110°C, 4h; R = OMe, Eaton's reagent, 80°C, 2h; (b) i nBuLi, 4-Br-C₆H₅-OTHP, THF; ii HCI, MeOH.(c) K₂CO₃, 1-(2-chloroethyl)pyrrolidine hydrochloride, acetone, 24h, 85°C;(d) PyHBr₃, CH₂ Cl₂, 20°, 18th; (e) Pd(PPh₃)₃, 4-HOC₆H₅B(OH)₂, Na₂CO₃(aq), THF; (f) BBr₃, CH₂Cl₂.

Table I.  Antiproliferative effects and estrogen receptor binding affinities for benzothiepin type SERMs.

Compound	Yield (%)	MCF-7 IC50 (μM)^a	ERα/IC50 (nM)^b	ERβ/IC50 (nM)^b	ER β/α
6	52	1.584 ± 0.111	8.77	46.1	0.19
13a	72	0.0698 ± 0.006	8.4	3.8	2.21
13b	58	0.210 ± 0.167	9.1	2.4	3.79
13c	40	0.0185 ± 0.001	6.76	0.7	9.65
14	62	0.306 ± 0.003	10.0	6.5	1.54
Tamoxifen^c	–	4.12 ± 0.038	70	170	0.41

^aExperimental values represent the average for two experiments performed in triplicate along with the standard deviation (SD) between the assay values. Values without SD values were run once. IC₅₀ values are half maximal inhibitory concentrations required to block the growth stimulation of MCF-7 cells

^b Values are an average of at least nine replicate experiments for ERα with typical standard errors below 15%; and six replicate experiments for ERβ with typical standard errors below 15%

^cThe value for tamoxifen IC₅₀ 4.12 ± 0.38μM is in good agreement with the reported IC₅₀ value for tamoxifen using the MTT assay on human MCF-7 cells.

Scheme 2 Synthesis of Benzothiepin 12c. Scheme reagents: (a) PyHBr₃, CH₂Cl₂, 20°, 18h; (b) K₂CO₃, 1-(2-chloroethyl)pyrrolidine hydrochloride, acetone, 24h, 85°C.

Table II.  Summary of key Ligand-Protein contacts^a.

Compound	Isoform	Asp 351 (Ala 257)	Glu 353 (Glu 260)	Arg 394 (Arg 301)	His 524 (His 430)
13c	α	4.7	2.8	2.5	3.0
13c	β	3.7	2.3	5.1	3.2

^aResidues depicted are those present in crystal structure 3ERT, except those in brackets denoting residues of crystal structure 1QKN. Bold font indicates H-bonding distances.

Figure 2 Docked complex of compound 13c in active site of ERα and ERβ superposed.