Optimization of Hydroxybenzothiazoles as Novel Potent and Selective Inhibitors of 17β-HSD1

17β-HSD1 is a novel target for the treatment of estrogen-dependent diseases, as it catalyzes intracellular estradiol formation. Starting from two recently described compounds, highly active and selective inhibitors were developed. Benzoyl <b>6</b> and benzamide <b>17</b> are the most selective compounds toward 17β-HSD2 described so far. They also showed a promising profile regarding activity in T47-D cells, selectivity toward ERα and ERβ, inhibition of hepatic CYP enzymes, metabolic stability, and inhibition of marmoset 17β-HSD1 and 17β-HSD2

Interactions found in the complexes between 6, 21 and the five 17β-HSD1 crystal structures used to build up the pharmacophore, respectively.

a<p>Distance (Å) between the heteroatoms for H-bonds (H) and between centroids or centroid and cation for π-interactions (π).</p

Synthesis of compounds 19–25.

<p>Reagents and conditions: (a) pyridine, 100°C, 20 h, for <b>19i</b>: <i>p</i>-methoxybenzoylchloride, for <b>21i</b>: <i>m</i>-methoxybenzoylchloride, for <b>22i</b>: <i>m</i>-methoxyphenylsulfochloride, for compound <b>23i</b>: <i>m</i>-methoxybenzoisocyanate, for <b>24i</b>: <i>m</i>-methoxybenzoisothiocyanate, for compound <b>25i</b>: <i>m</i>-methoxybenzylchloride; (b) for <b>19–21</b>, BF₃S(CH₃)₂, anhydrous CH₂Cl₂, rt, 20 h; for <b>22–25</b>, BBr₃, CH₂Cl₂, −78°C to rt, 20 h.</p

Pharmacophoric features exploited by 6 and 21.

<p>Six for compound <b>6</b> (showed in A) and five for compound <b>21</b> (showed in B).</p

Synthesis of compounds 6–18.

<p>Reagents and conditions: (a) 1) NaNO₂, H₃PO₄ (85%), −10°C, 20 min, 2) H₃PO₂, H₃PO₄ (85%), −10°C to rt, 20 h; (b) 1) nBuLi, anhydrous THF, −70°C to −20°C, 1 h, 2) for <b>6ii</b> and <b>12ii</b>: <i>m</i>-methoxybenzaldehyde, for <b>9ii</b>: <i>p</i>-methoxybenzaldehyde, for <b>15i</b>: <i>o</i>-methoxybenzoisocyanate, for <b>17i</b>: <i>m</i>-methoxybenzoisocyanate, anhydrous THF, −15°C, 90 min; (c) for <b>6i</b>, <b>12i</b> and <b>13i</b>, SIBX, anhydrous THF, 0°C to 60°C, 20 h; for <b>10</b> and <b>11i</b>: TMSiCl, NaI, CH₃CN, reflux, 20 h; (d) for <b>6–9</b> and <b>15–18</b>: BF₃S(CH₃)₂, anhydrous CH₂Cl₂, rt, 20 h; for compounds <b>11–14</b>, pyridinium hydrochloride, 220°C, 4 h.</p

Pharmacophore model.

<p>The pharmacophoric features derived from the ligands are rendered as dotted spheres and are color-coded: dark orange for aromatic ring and aromatic ring projection (<b>HY1</b> and <b>HY5</b>), green for hydrophobic regions (<b>HY2-HY4</b>) and magenta for acceptor and donor atom features (<b>AD1-AD3</b> and <b>D4</b>). The identified aromatic ring projection <b>HY6</b> as well as the donor projection feature <b>D7</b> is not exploited by steroidal inhibitors. The protein-derived acceptor or donor features (<b>A1a</b>, <b>D1b</b>, <b>AD2a</b>, <b>AD2b</b>, <b>A3a</b>, <b>D4a</b>, <b>D4b</b>, <b>AD5a</b>, <b>AD5b</b>, <b>D6a</b> and <b>A6b</b>) and the aromatic ring projection <b>P5</b> are depicted as yellow, meshed spheres.</p

Pharmacophore derived complex between 17β-HSD1 (PDB-ID: 1equ) and compound 6 (dark orange).

<p>NADP⁺ (green), interacting residues (blue), potential interacting residues (black) and ribbon rendered tertiary structure of the active site are shown.</p

Steroidal ligands co-crystallized with 17β-HSD1.

<p>The five steroidal ligands cocrystalized with 17β-HSD1s that were used to build the pharmacophore model. Structural information was taken from the protein data bank(PDB-ID: 1a27, 1equ, 1dht, 1i5r, and 3hb5, respectively).</p

Rigidification strategy.

<p>Rigidification strategy.</p

Nonsteroidal 17β-HSD1 inhibitors published by our group.

<p>Nonsteroidal 17β-HSD1 inhibitors published by our group.</p