Antibiotics have been effective tools in the treatment of infectious diseases during the last half-century. From the development of antibiotic therapy to the late 1980s there was almost complete control over bacterial infections in developed countries. However, in response to the pressure of antibiotic usage, multiple resistance mechanisms have become widespread and are threatening the clinical utility of antibacterial therapy. The increase in antibiotic resistant strains has been particularly common in major hospitals and care centers. The consequences of the increase in resistant strains include higher morbidity and mortality, longer patient hospitalization, and an increase in treatment costs

[0003] Various bacteria have evolved β-lactam deactivating enzymes, namely, β-lactamases, that counter the efficacy of the various β-lactams. β-lactamases can be grouped into 4 classes based on their amino acid sequences, namely, Ambler classes A, B, C, and D. Enzymes in classes A, C, and D include active-site serine β-lactamases, and class B enzymes, which are encountered less frequently, are Zn-dependent. These enzymes catalyze the chemical degradation of β-lactam antibiotics, rendering them inactive. Some β-lactamases can be transferred within and between various bacterial strains and species. The rapid spread of bacterial resistance and the evolution of multi- resistant strains severely limits β-lactam treatment options available.

[0004] The increase of class D β-lactamase-expressing bacterium strains such as Acinetobacter baumannii has become an emerging multidrug-resistant threat. A. baumannii strains express A, C, and D class β-lactamases. The class D β-lactamases such as the OXA families are particularly effective at destroying carbapenem type β-lactam antibiotics, e.g., imipenem, the active carbapenems component of Merck’s Primaxin® (Montefour, K.; et al. Crit. Care Nurse 2008, 28, 15; Perez, F. et al. Expert Rev. Anti Infect. Ther. 2008, 6, 269; Bou, G.; Martinez-Beltran, J. Antimicrob. Agents Chemother. 2000, 40, 428. 2006, 50, 2280; Bou, G. et al, J. Antimicrob. Agents Chemother. 2000, 44, 1556). This has imposed a pressing threat to the effective use of drugs in that category to treat and prevent bacterial infections. Indeed the number of catalogued serine-based β- lactamases has exploded from less than ten in the 1970s to over 300 variants. These issues fostered the development of five “generations” of cephalosporins. When initially released into clinical practice, extended- spectrum cephalosporins resisted hydrolysis by the prevalent class A β-lactamases, TEM-1 and SHV-1. However, the development of resistant strains by the evolution of single amino acid substitutions in TEM-1 and SHV-1 resulted in the emergence of the extended- spectrum β-lactamase (ESBL) phenotype.

[0005] New β-lactamases have recently evolved that hydrolyze the carbapenem class of antimicrobials, including imipenem, biapenem, doripenem, meropenem, and ertapenem, as well as other β-lactam antibiotics. These carbapenemases belong to molecular classes A, B, and D. Class A carbapenemases of the KPC-type predominantly in Klebsiella pneumoniae but now also reported in other Enterobacteriaceae, Pseudomonas aeruginosa and Acinetobacter baumannii. The KPC carbapenemase was first described in 1996 in North Carolina, but since then has disseminated widely in the US. It has been particularly problematic in the New York City area, where several reports of spread within major hospitals and patient morbidity have been reported. These enzymes have also been recently reported in France, Greece, Sweden, United Kingdom, and an outbreak in Germany has recently been reported. Treatment of resistant strains with carbapenems can be associated with poor outcomes.

[0006] Another mechanism of β-lactamase mediated resistance to carbapenems involves combination of permeability or efflux mechanisms combined with hyper production of beta-lactamases. One example is the loss of a porin combined in hyperproduction of ampC beta-lactamase results in resistance to imipenem in Pseudomonas aeruginosa. Efflux pump over expression combined with hyperproduction of the ampC β-lactamase can also result in resistance to a carbapenem such as meropenem.

[0007] Because there are three major molecular classes of serine-based β- lactamases, and each of these classes contains significant numbers of β-lactamase variants, inhibition of one or a small number of β-lactamases is unlikely to be of therapeutic value. Legacy β-lactamase inhibitors are largely ineffective against at least Class A carbapenemases, against the chromosomal and plasmid-mediated Class C cephalosporinases and against many of the Class D oxacillinases. Therefore, there is a need for improved β-lactamase inhibitors.

The following compounds are prepared starting from enantiomerically pure (R)-tert-butyl 3-hydroxypent-4-enoate (J. Am. Chem. Soc. 2007, 129, 4175-4177) in accordance with the procedure described in the above Example 1.

5

[0175] 2-((3R,6S)-2-hydroxy-3-(2-(thiophen-2-yl)acetamido)-l,2-oxaborinan-6- yl)acetic acid 5. 1H NMR (CD₃OD) δ ppm 0.97-1.11 (q, 1H), 1.47-1.69 (m, 2H), 1.69-1.80 (m, 1H), 2.21-2.33 (td, 1H), 2.33-2.41 (dd, 1H), 2.58-2.67 (m, 1H), 3.97 (s, 2H), 4.06-4.14 (m, 1H), 6.97-7.04 (m, 1H), 7.04-7.08 (m, 1H), 7.34-7.38 (dd, 1H); ESIMS found for Ci₂Hi₆BN0₅S m/z 280 (100%) (M-H₂0)⁺.

EXAMPLES

Example 1 – Synthesis of Intermediate Compound 10

[0191] The compound of Formula 10 was synthesized as shown in Scheme 3, below:

Scheme 3

95%

80% for 2 steps

(i?)-t-butyl 3-(trimethysilyloxy)-pent-4-enoate (7)

[0192] Chlorotrimethylsilane (4.6 mL, 36.3 mmol, 1.25 eq) was added to a solution of (R)-t-butyl 3-hydroxy-pent-4-enoate (1, 5 g, 29 mmol) and triethylamine (5.3 mL, 37.3 mmol, 1.3 eq) in dichloromethane (25 mL) keeping the temperature below 30 °C. After completion of the addition, the white heterogeneous mixture was stirred at rt for 20 minutes (TLC, GC, note 2) then quenched with MeOH (352 μί, 0.3 eq). After stirring at rt for 5 minutes, the white heterogeneous reaction mixture was diluted with heptane (25 mL). The salts were filtered off and rinsed with heptane (2 x 10 mL). The combined turbid filtrates were washed with a saturated solution of NaHC0₃ (2 x 25 mL) and concentrated to dryness. The residual oil was azeotroped with heptane (25 mL) to give a colorless oil that was used immediately.

QSVt-butyl 3-(trimethylsilyloxy)-5-(4,4,5,5-tetramethyl-[L3,21dioxaborolan-2-yl)-pentanoate (8)

[0193] A solution of bis-diphenylphosphino-ethane (46.3 mg, 0.2 mol%) and [Ir(COD)Cl]2 (39 mg, 0.1 mol%) in CH2C12 (5 mL) was added to a refluxing solution of crude TMS-protected pentenoate 7. Pinacol borane (9.3 mL,l .l eq) was added to the

refluxing solution. After stirring at reflux for 3 h, the reaction mixture was cooled to room temperature, concentrated to dryness and taken up in heptane (50 mL). The insolubles were filtered over Celite and rinse with heptane (10 mL).

Ethanolamine-boronic acid salt (10)

[0194] A mixture of fully protected boronate 8 (5.0 g, 13.4 mmol), 0.5 N HC1 (5 mL) and acetone (0.5 mL) was stirred vigorously at room temperature, providing intermediate 9. After complete consumption of the starting material, a solution of NaI0₄ (3.44 g, 1.2 eq) in water (15 mL) was added slowly keeping the temperature <30 °C. Upon the completion of the addition (30 min), the reaction mixture was allowed to cool to room temperature. After consumption of all pinacol, MTBE (5 mL) was added. After stirring at room temperature for 10 min, the white solids were filtered off and rinsed with MTBE (2 x 5 mL). The filtrate was partitioned and the aqueous layer was extracted with MTBE (10 mL). The combined organic extracts were washed sequentially with a 0.1 M NaHS0₃ solution (2 x 5 mL), a saturated NaHC0₃ solution (5 mL) and brine (5 mL). The organic layer was concentrated to dryness. The residue was taken up in MTBE (15 mL) and the residual salts filtered off. The filtrate was concentrated to dryness and the residue was taken up in MTBE (10 mL) and acetonitrile (1.7 mL). Ethanolamine (0.99 mL, 1.1 eq) was added. After stirring at room temperature for 1 hour, the heterogeneous mixture was stirred at 0 °C. After stirring at 0 °C for 2 hours, the solids were collected by filtration, rinsed with MTBE (2 x 5 mL), air dried then dried under high vacuum to give Compound 10 as a white granular powder.

Example 2 – Preparation of Beta-Lactamase Inhibitor (15)

[0195] The compound of Formula 15 was synthesized as shown in Scheme 4 below:

Scheme 4

Synthesis of pinanediol boronate (12)

[0196] Ethanolammonium boronate 11 (15 g, 61.7 mmol) and pinanediol (10.5 g, 61.7 mmol, 1 eq) were suspended in MTBE (75 mL). Water (75 mL) was added and the yellow biphasic heterogeneous mixture was stirred at room temperature. After stirring for 2 hours at room temperature, some pinanediol was still present and stirring was continued overnight. The layers were separated and the organic layer was washed with brine, concentrated under reduced pressure and azeotroped with MTBE (2 x 30 mL). The residual oil was taken up in dichloromethane (40 mL). In another flask, TBSC1 (1 1.6 g, 77.1 mmol, 1.25 eq) was added to a solution of imidazole (9.66 g, 141.9 mmol, 2.3 eq) in dichloromethane (25 mL). The white slurry was stirred at room temperature. After 5 minutes, the solution of pinanediol boronate was added to the white slurry and the flask was rinsed with dichloromethane (2 x 5 mL). The heterogeneous reaction mixture was heated at reflux temeprature. After stirring at reflux for 8 hours, the reaction mixture was cooled to 30 °C and TMSC1 (330 \JL) was added. After stirring 30 minutes at 30 °C, MeOH (15 mL) was added. After stirring at room temperature overnight, the reaction mixture was washed sequentially with 0.5 N HC1 (115 niL), 0.5 N HC1 (60 n L) and saturated NaHC0₃ (90 niL). The organic layer was concentrated under reduced pressure and azeotroped with heptane (150 n L) to give 12 as a yellow oil (27.09 g, 94.1%) which was used without purification.

Synthesis of chloroboronate (13)

[0197] A solution of n-butyllithium (2.5 M in hexane, 29.6 niL, 74.1 mmol, 1.3 eq) was added to THF (100 mL) at -80 °C. The resulting solution was cooled to -100 °C. A solution of dichloromethane (14.6 mL, 228 mmol, 4 eq) in THF (25 mL) was added via syringe pump on the sides of the flask keeping the temperature < -95 °C. During the second half of the addition a precipitate starts to appear which became thicker with the addition of the remaining dichloromethane solution. After stirring between -100 and -95 °C for 30 min, a solution of 12 (26.59 g, 57 mmol) in THF (25 mL) was added by syringe pump on the sides of the flask while maintaining the batch temperature < -95 °C to give a clear yellow solution. After stirring between -100 and -95 °C for 30 min, a solution of zinc chloride (1 M in ether, 120 mL, 120 mmol, 2.1 eq) was added keeping the temperature < -70 °C. The reaction mixture was then warmed to room temperature (at about -18 °C the reaction mixture became turbid/heterogeneous). After stirring at room temperature for 2 hours, the reaction mixture was cooled to 15 °C and quenched with 1 N HC1 (100 mL). The layers were separated and the organic layer was washed sequentially with 1 N HC1 (100 mL) and water (2 x 100 mL), concentrated to oil and azeotroped with heptane (3 x 150 mL) to provide 13 as a yellow oil (30.03 g, 102%) which was used without purification.

Synthesis of (14)

[0198] LiHMDS (1 M in THF, 63 mL, 62.7 mmol, 1.1 eq) was added to a solution of 13 (29.5 g, 57 mmol) in THF (60 mL) while maintaining the batch temperature at < -65 °C. After stirring at -78 °C for 2 hours, additional LiHMDS (5.7 mL, 0.1 eq) was added to consume the remaining starting material. After stirring at -78 °C for 30 minutes, the tan reaction mixture was warmed to room temperature. After stirring at room temperature for one hour, the solution of silylated amine was added via cannula to a solution of HOBT ester of 2-thienylacetic acid in acetonitrile at 0 °C (the solution of HOBT ester was prepared by adding EDCI (16.39 g, 85.5 mmol, 1.5 eq) to a suspension of recrystallized 2-thienylacetic acid (9.73 g, 68.4 mmol, 1.2 eq) and HOBT.H₂0 (11.35 g, 74.1 mmol, 1.3 eq) in acetonitrile (10 mL) at 0 °C. The clear solution was stirred at 0 °C for 30 minutes prior to the addition of the silylated amine). After stirring at 0 °C for one hour, the heterogeneous reaction mixture was placed in the fridge overnight. Saturated aqueous sodium bicarbonate (80 mL) and heptane (80 mL) were added, and after stirring 30 minutes at room temperature, the layers were separated. The organic layer was washed with saturated aqueous sodium bicarbonate (2 x 80 mL) and filtered through Celite. The filtrate was concentrated under reduced pressure and the tan oil was azeotroped with heptane (3 x 1 10 mL). The residue was taken up in heptane (60 mL) and seeds were added. After stirring at room temperature for one hour, the reaction mixture became heterogeneous. After stirring 4 hours at 0 °C, the solids were collected by filtration and washed with ice cold heptane (3 x 20 mL), air dried then dried under high vacuum to give 14 as an off white powder (10.95 g, 31%).

Synthesis of (15)

[0199] A mixture of 14 (10 g, 16.1 mmol), boric acid (1.3 g, 20.9 mmol, 1.3 eq), dioxane (20 mL), and 1 M sulfuric acid (10 mL) was heated at 75 °C. After stirring 7 hours at 75 °C, the cooled reaction mixture was diluted with water (10 mL) and MTBE (30 mL) and the residual mixture was cooled to 0 °C. The pH was adjusted to 5.0 with a solution of 2 N NaOH (14 mL). The layers were separated and the aqueous layer was extracted with MTBE (2 x 30 mL) then concentrated to dryness. The residue was taken up in water (10 mL) and the solution was filtered through a 0.45 μηι GMF syringe filter. The flask and filter were rinsed with water (7.5 mL). The pH of the filtrate was lowered to 4.0 with 2 M H₂SO₄ and seeds (5 mg) were added. After stirring at room temperature for 10 minutes, the pH was lowered to 1.9 over 1 hour with 2 M H₂S0₄ (total volume 3.5 mL). After stirring at room temperature for 2 hours, the solids were collected by filtration. The filtrate was recirculated twice to rinse the flask and the cake was washed with water (2 x 12 mL), air dried then dried under high vacuum to give 15 as a white powder (3.63 g, 76%).