C25-modified rifamycin derivatives with improved activity against Mycobacterium abscessus.

Infections caused by Mycobacterium abscessus are difficult to treat due to its intrinsic resistance to most antibiotics. Formation of biofilms and the capacity of M. abscessus to survive inside host phagocytes further complicate eradication. Herein, we explored whether addition of a carbamate-linked group at the C25 position of rifamycin SV blocks enzymatic inactivation by ArrMab, an ADP-ribosyltransferase conferring resistance to rifampicin (RMP). Unlike RMP, 5j, a benzyl piperidine rifamycin derivative with a morpholino substituted C3 position and a naphthoquinone core, is not modified by purified ArrMab. Additionally, we show that the ArrMab D82 residue is essential for catalytic activity. Thermal profiling of ArrMab in the presence of 5j, RMP, or rifabutin shows that 5j does not bind to ArrMab. We found that the activity of 5j is comparable to amikacin against M. abscessus planktonic cultures and pellicles. Critically, 5j also exerts potent antimicrobial activity against M. abscessus in human macrophages and shows synergistic activity with amikacin and azithromycin.

Rifamycin derivatives active against pathogenic rapidly-growing mycobacteria.

Infections due to rapidly growing mycobacteria (RGM), and in particular the RGM species Mycobacterium abscessus (Mab), are very difficult to treat and reports on novel therapeutic options are scarce. A hallmark of all pathogenic RGM species is their resistance to the four first-line drugs used to treat infections with Mycobacterium tuberculosis including rifampicin. This study demonstrates that modification of the rifampicin scaffold can restore rifampicin activity against the three most commonly isolated pathogenic RGM species including Mab. We also note that the structure-activity relationship for Mab is different as compared to the non-pathogenic RGM species Mycobacterium smegmatis.

Structure-based design and optimization of potent inhibitors of the adenoviral protease.

Adenoviral infections are associated with a wide range of acute diseases, among which ocular viral conjunctivitis (EKC) and disseminated disease in immunocompromised patients. To date, no approved specific anti-adenoviral drug is available, but there is a growing need for an effective treatment of such infections. The adenoviral protease, adenain, plays a crucial role for the viral lifecycle and thus represents an attractive therapeutic target. Structure-guided design with the objective to depeptidize tetrapeptide nitrile 1 led to the novel chemotype 2. Optimization of scaffold 2 resulted in picomolar adenain inhibitors 3a and 3b. In addition, a complementary series of irreversible vinyl sulfone containing inhibitors were rationally designed, prepared and evaluated against adenoviral protease. High resolution X-ray co-crystal structures of representatives of each series proves the successful design of these inhibitors and provides an excellent basis for future medicinal chemistry optimization of these compounds.

Discovery and structure-based optimization of adenain inhibitors.

The cysteine protease adenain is the essential protease of adenovirus and, as such, represents a promising target for the treatment of ocular and other adenoviral infections. Through a concise two-pronged hit discovery approach we identified tetrapeptide nitrile 1 and pyrimidine nitrile 2 as complementary starting points for adenain inhibition. These hits enabled the first high-resolution X-ray cocrystal structures of adenain with inhibitors bound and revealed the binding mode of 1 and 2. The screening hits were optimized by a structure-guided medicinal chemistry strategy into low nanomolar drug-like inhibitors of adenain.

In vivo optimization of 2,3-diaminopyrazine Rho Kinase inhibitors for the treatment of glaucoma.

A series of 2,3,6-pyrazine Rho Kinase inhibitors were optimized for in vivo activity for topical ocular dosing. Modifications of the 2-(piperazin-1-yl)pyrazine derivatives produced compounds with improved solubility and physicochemical properties. Modifications of the 6-pyrazine substituent led to improvements in in vitro potency. Compound 9 had the best in vitro and in vivo potency of EC50=260 nM with a 30% reduction of IOP in a non-human primate model at a dose of 0.33%.

Discovery and early clinical evaluation of BMS-605339, a potent and orally efficacious tripeptidic acylsulfonamide NS3 protease inhibitor for the treatment of hepatitis C virus infection.

The discovery of BMS-605339 (35), a tripeptidic inhibitor of the NS3/4A enzyme, is described. This compound incorporates a cyclopropylacylsulfonamide moiety that was designed to improve the potency of carboxylic acid prototypes through the introduction of favorable nonbonding interactions within the S1' site of the protease. The identification of 35 was enabled through the optimization and balance of critical properties including potency and pharmacokinetics (PK). This was achieved through modulation of the P2* subsite of the inhibitor which identified the isoquinoline ring system as a key template for improving PK properties with further optimization achieved through functionalization. A methoxy moiety at the C6 position of this isoquinoline ring system proved to be optimal with respect to potency and PK, thus providing the clinical compound 35 which demonstrated antiviral activity in HCV-infected patients.

Respiratory syncytial virus fusion inhibitors. Part 7: structure-activity relationships associated with a series of isatin oximes that demonstrate antiviral activity in vivo.

A series of bezimidazole-isatin oximes were prepared and profiled as inhibitors of respiratory syncytial virus (RSV) replication in cell culture. Structure-activity relationship studies were directed toward optimization of antiviral activity, cell permeability and metabolic stability in human liver micorosomes (HLM). Parallel combinatorial synthetic chemistry was employed to functionalize isatin oximes via O-alkylation which quickly identified a subset of small, lipophilic substituents that established good potency for the series. Further optimization of the isatin oxime derivatives focused on introduction of nitrogen atoms to the isatin phenyl ring to provide a series of aza-isatin oximes with significantly improved PK properties. Several aza-isatin oximes analogs displayed targeted metabolic stability in HLM and permeability across a confluent monolayer of CaCo-2 cells. These studies identified several compounds, including 18i, 18j and 18n that demonstrated antiviral activity in the BALB/c mouse model of RSV infection following oral dosing.

Respiratory syncytial virus fusion inhibitors. Part 6: an examination of the effect of structural variation of the benzimidazol-2-one heterocycle moiety.

The effect of structural variation of the benzimidazol-2-one ring of RSV fusion inhibitors related to BMS-433771 (1) was examined in conjunction with side chain modifications and the introduction of an aminomethyl substituent at the 5-position of the core benzimidazole moiety. Replacement of the benzimidazol-2-one moiety with benzoxazole, oxindole, quinoline-2-one, quinazolin-2,4-dione and benzothiazine derivatives provided a series of potent RSV fusion inhibitors 4. However, the intrinsic potency of 6,6-fused ring systems was generally less than that of comparably substituted 5,6-fused heterocycles of the type found in BMS-433771 (1). The introduction of an aminomethyl substituent to the benzimidazole ring enhanced antiviral activity in the 6,6-fused ring systems.

Respiratory syncytial virus fusion inhibitors. Part 5: Optimization of benzimidazole substitution patterns towards derivatives with improved activity.

Extensive SAR studies and optimization of ADME properties of benzimidazol-2-one derivatives led to the identification of BMS-433771 (3) as an orally active RSV fusion inhibitor. In order to extend the structure-activity relationships for this compound series, substitution of the benzimidazole ring was examined with a view to establishing additional productive interactions between the inhibitor and functionality present in the proposed binding pocket. Amongst the compounds synthesized, the 5-aminomethyl analogue 10aa demonstrated potent antiviral activity towards wild-type RSV and retained excellent inhibitory activity towards a virus that had been developed to express resistance to BMS-433771 (3), data consistent with an additional productive interaction between the inhibitor and the fusion protein target.

Respiratory syncytial virus fusion inhibitors. Part 4: optimization for oral bioavailability.

A series of benzimidazole-based inhibitors of respiratory syncytial virus (RSV) fusion were optimized for antiviral potency, membrane permeability and metabolic stability in human liver microsomes. 1-Cyclopropyl-1,3-dihydro-3-[[1-(4-hydroxybutyl)-1H-benzimidazol-2-yl]methyl]-2H-imidazo[4,5-c]pyridin-2-one (6m, BMS-433771) was identified as a potent RSV inhibitor demonstrating good bioavailability in the mouse, rat, dog and cynomolgus monkey that demonstrated antiviral activity in the BALB/c and cotton rat models of infection following oral administration.

Synthesis and antibacterial evaluation of a novel series of rifabutin-like spirorifamycins.

A novel series of spirorifamycins was synthesized and their antibacterial activity evaluated both in vitro and in vivo. This new series of rifamycins shows excellent activity against Staphylococcus aureus that is equivalent to rifabutin. However, some compounds of the series exhibit lower MICs than rifabutin against rifampin-resistant strains of S. aureus. Further, compound 2e exhibits comparable efficacy in vivo in a murine model of S. aureus septicemia model following administration by either oral or parenteral dosing routes.

New C25 carbamate rifamycin derivatives are resistant to inactivation by ADP-ribosyl transferases.

A novel series of 3-morpholino rifamycins in which the C25 acetate group was replaced by a carbamate group were prepared and found to exhibit significantly improved antimicrobial activity than rifampin against Mycobacterium smegmatis. Further characterization of such compounds suggests that relatively large groups attached to the rifamycin core via a C25 carbamate linkage prevent inactivation via ribosylation of the C23 alcohol as catalyzed by the endogenous rifampin ADP-ribosyl transferase of M. smegmatis. SAR studies of the C25 carbamate rifamycin series against M. smegmatis and other bacteria are reported.

Respiratory syncytial virus fusion inhibitors. Part 3: Water-soluble benzimidazol-2-one derivatives with antiviral activity in vivo.

The introduction of acidic and basic functionality into the side chains of respiratory syncytial virus (RSV) fusion inhibitors was examined in an effort to identify compounds suitable for evaluation in vivo in the cotton rat model of RSV infection following administration as a small particle aerosol. The acidic compounds 2r, 2u, 2v, 2w, 2z, and 2aj demonstrated potent antiviral activity in cell culture and exhibited efficacy in the cotton rat comparable to ribavirin. In a BALB/c mouse model, the oxadiazolone 2aj reduced virus titers following subcutaneous dosing, whilst the ester 2az and amide 2aab exhibited efficacy following oral administration. These results established the potential of this class of RSV fusion inhibitors to interfere with infection in vivo following topical or systemic administration.

Oral efficacy of a respiratory syncytial virus inhibitor in rodent models of infection.

BMS-433771 is a potent inhibitor of respiratory syncytial virus (RSV) replication in vitro. Mechanism of action studies have demonstrated that BMS-433771 halts virus entry through inhibition of F protein-mediated membrane fusion. BMS-433771 also exhibited in vivo efficacy following oral administration in a mouse model of RSV infection (C. Cianci, K. Y. Yu, K. Combrink, N. Sin, B. Pearce, A. Wang, R. Civiello, S. Voss, G. Luo, K. Kadow, E. Genovesi, B. Venables, H. Gulgeze, A. Trehan, J. James, L. Lamb, I. Medina, J. Roach, Z. Yang, L. Zadjura, R. Colonno, J. Clark, N. Meanwell, and M. Krystal, Antimicrob. Agents Chemother. 48:413-422, 2004). In this report, the in vivo efficacy of BMS-433771 against RSV was further examined in the BALB/c mouse and cotton rat host models of infection. By using the Long strain of RSV, prophylactic efficacy via oral dosing was observed in both animal models. A single oral dose, administered 1 h prior to intranasal RSV inoculation, was as effective against infection as a 4-day b.i.d. dosing regimen in which the first oral dose was given 1 h prior to virus inoculation. Results of dose titration experiments suggested that RSV infection was more sensitive to inhibition by BMS-433771 treatment in the BALB/c mouse host than in the cotton rat. This was reflected by the pharmacokinetic and pharmacodynamic analysis of the efficacy data, where the area under the concentration-time curve required to achieve 50% of the maximum response was approximately 7.5-fold less for mice than for cotton rats. Inhibition of RSV by BMS-433771 in the mouse is the result of F1-mediated inhibition, as shown by the fact that a virus selected for resistance to BMS-433771 in vitro and containing a single amino acid change in the F1 region was also refractory to treatment in the mouse host. BMS-433771 efficacy against RSV infection was also demonstrated for mice that were chemically immunosuppressed by cyclophosphamide treatment, indicating that compound inhibition of the virus did not require an active host immune response.

Respiratory syncytial virus inhibitors. Part 2: Benzimidazol-2-one derivatives.

Structure-activity relationships for a series of benzimidazol-2-one-based inhibitors of respiratory syncytial virus are described. These studies focused on structural variation of the benzimidazol-2-one substituent, a vector inaccessible in a series of benzotriazole derivatives on which 2 is based, and revealed a broad tolerance for substituent size and functionality.

Orally active fusion inhibitor of respiratory syncytial virus.

BMS-433771 was found to be a potent inhibitor of respiratory syncytial virus (RSV) replication in vitro. It exhibited excellent potency against multiple laboratory and clinical isolates of both group A and B viruses, with an average 50% effective concentration of 20 nM. Mechanism-of-action studies demonstrated that BMS-433771 inhibits the fusion of lipid membranes during both the early virus entry stage and late-stage syncytium formation. After isolation of resistant viruses, resistance was mapped to a series of single amino acid mutations in the F1 subunit of the fusion protein. Upon oral administration, BMS-433771 was able to reduce viral titers in the lungs of mice infected with RSV. This new class of orally active RSV fusion inhibitors offers potential for clinical development.

Non-HIV antivirals - a review of the recent patent literature.

This review covers the non-HIV antiviral patent literature from December 2001 to April 2002. Most of the patent applications describe new compounds for the treatment of hepatitis C virus (HCV) by inhibition of the NS3 serine protease. Several examples of both nucleoside and non-nucleoside inhibitors of the HCV polymerase NS5B have been reported. Hepatitis B virus (HBV) therapy continues to be dominated by nucleoside analogs, but several non-nucleoside HBV polymerase inhibitors have also been reported. In addition, a number of patents describing non-nucleoside inhibitors of the human cytomegalovirus (HCMV), the herpes simplex virus (HSV-1 and HSV-2) and the varicella zoster virus (VZV) DNA polymerase are also reviewed. A number of patents that appeared in 2002 hold promise for the treatment of respiratory syncytial virus (RSV) with small molecule inhibitors. Various approaches to the treatment of hepatitis D virus (HDV), picornaviruses and the human papilloma virus (HPV) are also described.