Synthesis and evaluation of 3-(dihydroxyboryl)benzoic acids as D,D-carboxypeptidase R39 inhibitors.

Penicillin binding proteins (PBPs) catalyze steps in the biosynthesis of bacterial cell walls and are the targets for the beta-lactam antibiotics. Non-beta-lactam based antibiotics that target PBPs are of interest because bacteria have evolved resistance to the beta-lactam antibiotics. Boronic acids have been developed as inhibitors of the mechanistically related serine beta-lactamases and serine proteases; however, they have not been explored extensively as PBP inhibitors. Here we report aromatic boronic acid inhibitors of the D,D-carboxypeptidase R39 from Actinomadura sp. strain. Analogues of an initially identified inhibitor [3-(dihydroxyboryl)benzoic acid 1, IC(50) 400 microM] were prepared via routes involving pinacol boronate esters, which were deprotected via a two-stage procedure involving intermediate trifluorborate salts that were hydrolyzed to provide the free boronic acids. 3-(Dihydroxyboryl)benzoic acid analogues containing an amide substituent in the meta, but not ortho position were up to 17-fold more potent inhibitors of the R39 PBP and displayed some activity against other PBPs. These compounds may be useful for the development of even more potent boronic acid based PBP inhibitors with a broad spectrum of antibacterial activity.

Anticancer steroid sulfatase inhibitors: synthesis of a potent fluorinated second-generation agent, in vitro and in vivo activities, molecular modeling, and protein crystallography.

An improved steroid sulfatase inhibitor was prepared by replacing the N-propyl group of the second-generation steroid-like inhibitor (2) with a N-3,3,3-trifluoropropyl group to give (10). This compound is 5-fold more potent in vitro, completely inhibits rat liver steroid sulfatase activity after a single oral dose of 0.5 mg/kg, and exhibits a significantly longer duration of inhibition over (2). These biological properties are attributed to the increased lipophilicity and metabolic stability of (10) rendered by its trifluoropropyl group and also the potential H-bonding between its fluorine atom(s) and Arg(98) in the active site of human steroid sulfatase. Like other sulfamates, (10) is expected to be sequestered, and transported by, erythrocytes in vivo because it inhibits human carbonic anhydrase II (hCAII) potently (IC(50), 3 nmol/L). A congener (4), which possesses a N-(pyridin-3-ylmethyl) substituent, is even more active (IC(50), 0.1 nmol/L). To rationalize this, the hCAII-(4) adduct, obtained by cocrystallization, reveals not only the sulfamate group and the backbone of (4) interacting with the catalytic site and the associated hydrophobic pocket, respectively, but also the potential H-bonding between the N-(pyridin-3-ylmethyl) group and Nepsilon(2) of Gln(136). Like (2), both (10) and its phenolic precursor (9) are non-estrogenic using a uterine weight gain assay. In summary, a highly potent, long-acting, and nonestrogenic steroid sulfatase inhibitor was designed with hCAII inhibitory properties that should positively influence in vivo behavior. Compound (10) and other related inhibitors of this structural class further expand the armory of steroid sulfatase inhibitors against hormone-dependent breast cancer.

Structural and mechanistic basis of penicillin-binding protein inhibition by lactivicins.

Beta-lactam antibiotics, including penicillins and cephalosporins, inhibit penicillin-binding proteins (PBPs), which are essential for bacterial cell wall biogenesis. Pathogenic bacteria have evolved efficient antibiotic resistance mechanisms that, in Gram-positive bacteria, include mutations to PBPs that enable them to avoid beta-lactam inhibition. Lactivicin (LTV; 1) contains separate cycloserine and gamma-lactone rings and is the only known natural PBP inhibitor that does not contain a beta-lactam. Here we show that LTV and a more potent analog, phenoxyacetyl-LTV (PLTV; 2), are active against clinically isolated, penicillin-resistant Streptococcus pneumoniae strains. Crystallographic analyses of S. pneumoniae PBP1b reveal that LTV and PLTV inhibition involves opening of both monocyclic cycloserine and gamma-lactone rings. In PBP1b complexes, the ring-derived atoms from LTV and PLTV show a notable structural convergence with those derived from a complexed cephalosporin (cefotaxime; 3). The structures imply that derivatives of LTV will be useful in the search for new antibiotics with activity against beta-lactam-resistant bacteria.

Modification of estrone at the 6, 16, and 17 positions: novel potent inhibitors of 17beta-hydroxysteroid dehydrogenase type 1.

The 17beta-hydroxysteroid dehydrogenases (17beta-HSDs) catalyze the interconversion between the oxidized and reduced forms of androgens and estrogens at the 17 position. The 17beta-HSD type 1 enzyme (17beta-HSD1) catalyzes the reduction of estrone to estradiol and is expressed in malignant breast cells. Inhibitors of this enzyme thus have potential as treatments for hormone dependent breast cancer. Here we report the syntheses and biological evaluation of novel inhibitors based on the estrone or estradiol template. These have been investigated by modification at the 6, 16 or 17 positions or combinations of these in order to gain information about structure-activity relationships by probing different areas in the enzyme active site. Activity data have been incorporated into a QSAR with predictive power, and the X-ray crystal structures of compounds 15 and 16c have been determined. Compound 15 has an IC50 of 320 nM for 17beta-HSD1 and is selective for 17beta-HSD1 over 17beta-HSD2. Three libraries of amides are also reported that led to the identification of inhibitors 19e and 20a, which have IC50 values of 510 and 380 nM respectively, and 20 h which, having an IC50 value of 37 nM, is the most potent inhibitor of 17beta-HSD1 reported to date. These amides are also selective for 17beta-HSD1 over 17beta-HSD2.

E-ring modified steroids as novel potent inhibitors of 17beta-hydroxysteroid dehydrogenase type 1.

17beta-Hydroxysteroid dehydrogenases (17beta-HSDs) are an important class of steroidogenic enzymes that regulate the bioavailability of active estrogens and androgens and are as yet a relatively unexploited therapeutic target. Based on our investigations and those of others, E-ring modified steroids were identified as a useful template for the design of inhibitors of 17beta-HSD type 1, an enzyme involved in the conversion of estrone into estradiol. The synthesis and biological evaluation of a new series of N- and C-substituted 1,3,5(10)-estratrien-[17,16-c]-pyrazoles and the corresponding SAR are discussed. Among the N-alkylated analogues, the most potent inhibitor was the 1'-methoxyethyl derivative, 41, with an IC(50) of 530 nM in T47-D human breast cancer cells. The X-ray crystal structure of the 1'-isobutyl derivative, was determined. Further optimization of the template using parallel synthesis resulted in a library of C5'-linked amides from which 73 emerged. This pyridylethyl amide had an IC(50) of 300 nM and its activity, with that of 41, suggests the importance of hydrogen bond acceptor groups in the pyrazole side chain. Both 41 and 73 displayed selectivity over 17beta-HSD type 2, and preliminary investigations showed 41 to be nonestrogenic in vitro in a luciferase reporter gene assay in contrast to the parent pyrazole 25. Molecular modeling studies, which support these findings, and a QSAR, the predictive power of which was demonstrated, are also presented.

Novel D-ring modified steroid derivatives as potent, non-estrogenic, steroid sulfatase inhibitors with in vivo activity.

In pursuit of novel steroid sulfatase (STS) inhibitors devoid of estrogenicity, several D-ring modified steroid derivatives were synthesised. In vitro evaluation of the compounds identified two highly potent inhibitors, 4a and 4b, which were 18 times more active than estrone-3-O-sulfamate (EMATE), both having IC(50) values of ca. 1nM. These 16,17-seco-estra-1,3,5(10)-triene-16,17-imide derivatives were synthesised from estrone, via the intermediate 1, which was easily alkylated, deprotected and sulfamoylated affording the final compounds in high yields. In order to assess their biological profile, the selected inhibitors were tested for their in vivo inhibitory potency and estrogenicity in ovariectomised rats. After an oral dose of 10mg/kg per day for 5 days, 4a and 4b were found to inhibit rat liver steroid sulfatase by 99%. They were also devoid of estrogenic activity in the uterine weight gain assay, indicating that these two leads have therapeutic potential for the treatment of hormone-dependent breast cancer.

D-ring modified estrone derivatives as novel potent inhibitors of steroid sulfatase.

A series of novel D-ring modified derivatives of estrone was synthesized and tested as inhibitors of steroid sulfatase (STS). The steroidal D-ring was cleaved via an iodoform reaction and thermal condensation of the resulting marrianolic acid derivative gave 16,17-seco-estra-1,3,5(10)-triene-16,17-imide derivatives, where a piperidinedione moiety is in place of the D-ring. This synthetic approach was found to give a higher overall yield than the literature method of Beckmann rearrangement. A range of alkyl side chains have been introduced on the nitrogen atom of the imido-ring and the corresponding 3-O-sulfamates synthesized. The new D-ring modified estrone derivatives bearing a propyl (39) and a 1-pyridin-3-ylmethyl (46) moiety had IC(50) values of 1 nM when tested in placental microsomes for the inhibition of STS. These compounds are therefore up to 18-fold more potent than EMATE, the very first highly potent irreversible steroidal STS inhibitor.