Chemical modification of capuramycins to enhance antibacterial activity

Prospects and challenges for the application of tissue engineering technologies in the treatment of bone infections

Osteomyelitis is a devastating disease caused by microbial infection in deep bone tissue. Its high recurrence rate and impaired restoration of bone deficiencies are major challenges in treatment. Microbes have evolved numerous mechanisms to effectively evade host intrinsic and adaptive immune attacks to persistently localize in the host, such as drug-resistant bacteria, biofilms, persister cells, intracellular bacteria, and small colony variants (SCVs). Moreover, microbial-mediated dysregulation of the bone immune microenvironment impedes the bone regeneration process, leading to impaired bone defect repair. Despite advances in surgical strategies and drug applications for the treatment of bone infections within the last decade, challenges remain in clinical management. The development and application of tissue engineering materials have provided new strategies for the treatment of bone infections, but a comprehensive review of their research progress is lacking. This review discusses the critical pathogenic mechanisms of microbes in the skeletal system and their immunomodulatory effects on bone regeneration, and highlights the prospects and challenges for the application of tissue engineering technologies in the treatment of bone infections. It will inform the development and translation of antimicrobial and bone repair tissue engineering materials for the management of bone infections.

Assessment of residual chlorine in soil microbial community using metagenomics

Chlorine-containing disinfectants have been widely used around the world for the prevention and control of the COVID-19 pandemic. However, at present, little is known about the impact of residual chlorine on the soil micro-ecological environment. Herein, we treated an experimental soil-plant-microbiome microcosm system by continuous irrigation with a low concentration of chlorine-containing water, and then analyzed the influence on the soil microbial community using metagenomics. After 14-d continuous chlorine treatment, there were no significant lasting effect on soil microbial community diversity and composition either in the rhizosphere or in bulk soil. Although metabolic functions of the rhizosphere microbial community were affected slightly by continuous chlorine treatment, it recovered to the original status. The abundance of several resistance genes changed by 7 d and recovered by 14 d. According to our results, the chlorine residue resulting from daily disinfection may present a slight long-term effect on plant growth (shoot length and fresh weight) and soil micro-ecology. In general, our study assisted with environmental risk assessments relating to the application ofchlorine-containing disinfectants and minimization of risks to the environment during disease control, such as COVID-19.

Advances in Key Drug Target Identification and New Drug Development for Tuberculosis

Tuberculosis (TB) is a severe infectious disease worldwide. The increasing emergence of drug-resistant Mycobacterium tuberculosis (Mtb) has markedly hampered TB control. Therefore, there is an urgent need to develop new anti-TB drugs to treat drug-resistant TB and shorten the standard therapy. The discovery of targets of drug action will lay a theoretical foundation for new drug development. With the development of molecular biology and the success of Mtb genome sequencing, great progress has been made in the discovery of new targets and their relevant inhibitors. In this review, we summarized 45 important drug targets and 15 new drugs that are currently being tested in clinical stages and several prospective molecules that are still at the level of preclinical studies. A comprehensive understanding of the drug targets of Mtb can provide extensive insights into the development of safer and more efficient drugs and may contribute new ideas for TB control and treatment.

Comprehensive review on mechanism of action, resistance and evolution of antimycobacterial drugs

Tuberculosis is one of the deadliest infectious diseases existing in the world since ancient times and still possesses serious threat across the globe. Each year the number of cases increases due to high drug resistance shown by Mycobacterium tuberculosis (Mtb). Available antimycobacterial drugs have been classified as First line, Second line and Third line antibiotics depending on the time of their discoveries and their effectiveness in the treatment. These antibiotics have a broad range of targets ranging from cell wall to metabolic processes and their non-judicious and uncontrolled usage in the treatment for years has created a significant problem called multi-drug resistant (MDR) tuberculosis. In this review, we have summarized the mechanism of action of all the classified antibiotics currently in use along with the resistance mechanisms acquired by Mtb. We have focused on the new drug candidates/repurposed drugs, and drug in combinations, which are in clinical trials for either treating the MDR tuberculosis more effectively or involved in reducing the time required for the chemotherapy of drug sensitive TB. This information is not discussed very adequately on a single platform. Additionally, we have discussed the recent technologies that are being used to discover novel resistance mechanisms acquired by Mtb and for exploring novel drugs. The story of intrinsic resistance mechanisms and evolution in Mtb is far from complete. Therefore, we have also discussed intrinsic resistance mechanisms of Mtb and their evolution with time, emphasizing the hope for the development of novel antimycobacterial drugs for effective therapy of tuberculosis.

DPAGT1 Inhibitors of Capuramycin Analogues and Their Antimigratory Activities of Solid Tumors

Capuramycin displays a narrow spectrum of antibacterial activity by targeting bacterial translocase I (MraY). In our program of development of new N-acetylglucosaminephosphotransferase1 (DPAGT1) inhibitors, we have identified that a capuramycin phenoxypiperidinylbenzylamide analogue (CPPB) inhibits DPAGT1 enzyme with an IC₅₀ value of 200 nM. Despite a strong DPAGT1 inhibitory activity, CPPB does not show cytotoxicity against normal cells and a series of cancer cell lines. However, CPPB inhibits migrations of several solid cancers including pancreatic cancers that require high DPAGT1 expression in order for tumor progression. DPAGT1 inhibition by CPPB leads to a reduced expression level of Snail but does not reduce E-cadherin expression level at the IC₅₀ (DPAGT1) concentration. CPPB displays a strong synergistic effect with paclitaxel against growth-inhibitory action of a patient-derived pancreatic adenocarcinoma, PD002: paclitaxel (IC₅₀: 1.25 μM) inhibits growth of PD002 at 0.0024-0.16 μM in combination with 0.10-2.0 μM CPPB (IC₅₀: 35 μM).

Venom alkaloids against Chagas disease parasite: search for effective therapies

Chagas disease is an important disease affecting millions of patients in the New World and is caused by a protozoan transmitted by haematophagous kissing bugs. It can be treated with drugs during the early acute phase; however, effective therapy against the chronic form of Chagas disease has yet to be discovered and developed. We herein tested the activity of solenopsin alkaloids extracted from two species of fire ants against the protozoan parasite Trypanosoma cruzi, the aetiologic agent of Chagas disease. Although IC₅₀ determinations showed that solenopsins are more toxic to the parasite than benznidazole, the drug of choice for Chagas disease treatment, the ant alkaloids presented a lower selectivity index. As a result of exposure to the alkaloids, the parasites became swollen and rounded in shape, with hypertrophied contractile vacuoles and intense cytoplasmic vacuolization, possibly resulting in osmotic stress; no accumulation of multiple kinetoplasts and/or nuclei was detected. Overexpressing phosphatidylinositol 3-kinase-an enzyme essential for osmoregulation that is a known target of solenopsins in mammalian cells-did not prevent swelling and vacuolization, nor did it counteract the toxic effects of alkaloids on the parasites. Additional experimental results suggested that solenopsins induced a type of autophagic and programmed cell death in T. cruzi. Solenopsins also reduced the intracellular proliferation of T. cruzi amastigotes in infected macrophages in a concentration-dependent manner and demonstrated activity against Trypanosoma brucei rhodesiense bloodstream forms, which is another important aetiological kinetoplastid parasite. The results suggest the potential of solenopsins as novel natural drugs against neglected parasitic diseases caused by kinetoplastids.

Structures of Bacterial MraY and Human GPT Provide Insights into Rational Antibiotic Design

The widespread emergence of antibiotic resistance in pathogens necessitates the development of antibacterial agents inhibiting underexplored targets in bacterial metabolism. One such target is phospho-MurNAc-pentapeptide translocase (MraY), an essential integral membrane enzyme that catalyzes the first committed step of peptidoglycan biosynthesis. MraY has long been considered a promising candidate for antibiotic development in part because it is the target of five classes of naturally occurring nucleoside inhibitors with potent in vivo and in vitro antibacterial activity. Although these inhibitors each have a nucleoside moiety, they vary dramatically in their core structures, and they have different activity properties. Until recently, the structural basis of MraY inhibition was poorly understood. Several recent structures of MraY and its human paralog, GlcNAc-1-P-transferase, have provided insights into MraY inhibition that are consistent with known inhibitor activity data and can inform rational drug design for this important antibiotic target.

Biosynthetic and Synthetic Strategies for Assembling Capuramycin-Type Antituberculosis Antibiotics

Mycobacterium tuberculosis (Mtb) has recently surpassed HIV/AIDS as the leading cause of death by a single infectious agent. The standard therapeutic regimen against tuberculosis (TB) remains a long, expensive process involving a multidrug regimen, and the prominence of multidrug-resistant (MDR), extensively drug-resistant (XDR), and totally drug-resistant (TDR) strains continues to impede treatment success. An underexplored class of natural products—the capuramycin-type nucleoside antibiotics—have been shown to have potent anti-TB activity by inhibiting bacterial translocase I, a ubiquitous and essential enzyme that functions in peptidoglycan biosynthesis. The present review discusses current literature concerning the biosynthesis and chemical synthesis of capuramycin and analogs, seeking to highlight the potential of the capuramycin scaffold as a favorable anti-TB therapeutic that warrants further development.

New drugs for the treatment of Mycobacterium tuberculosis infection

Tuberculosis presents a grave challenge to health, globally instigating 1.5 million mortalities each year. Following the breakthrough of first-line anti-TB medication, the number of mortalities reduced greatly; nonetheless, the swift appearance of tuberculosis which was drug-resistant, as well as the capability of the bacterium to survive and stay dormant are a considerable problem for public health. In order to address this issue, several novel possible candidates for tuberculosis therapy have been subjected to clinical trials of late. The novel antimycobacterial agents are acquired from different categories of medications, operate through a range of action systems, and are at various phases of advancement. We therefore talk about the present methods of treating tuberculosis and novel anti-TB agents with their action method, in order to advance awareness of these new compounds and medications.

New tuberculosis drug leads from naturally occurring compounds

Tuberculosis (TB) continues to be a significant cause of mortality and morbidity worldwide. An estimated 2 billion individuals are infected with Mycobacterium tuberculosis and annually there are approximately 10 million new cases of clinical TB and 1.5 million deaths. Currently available drugs and vaccines have had no significant impact on TB control. In addition, the emergence of drug resistant TB is considered a public health crisis, with some strains now resistant to all available drugs. Unfortunately, the growing burden of antibiotic resistance is coupled with decreased effort in the development of new antibiotics. Natural sources are attractive starting points in the search for anti-tubercular drugs because they are extremely rich in chemical diversity and have privileged antimicrobial activity. This review will discuss recent advances in the development of TB drug leads from natural products, with a particular focus on anti-mycobacterial compounds in late-stage preclinical and clinical development.

Nucleoside Derived Antibiotics to Fight Microbial Drug Resistance: New Utilities for an Established Class of Drugs?

Novel antibiotics are urgently needed to combat the rise of infections due to drug-resistant microorganisms. Numerous natural nucleosides and their synthetically modified analogues have been reported to have moderate to good antibiotic activity against different bacterial and fungal strains. Nucleoside-based compounds target several crucial processes of bacterial and fungal cells such as nucleoside metabolism and cell wall, nucleic acid, and protein biosynthesis. Nucleoside analogues have also been shown to target many other bacterial and fungal cellular processes although these are not well characterized and may therefore represent opportunities to discover new drugs with unique mechanisms of action. In this Perspective, we demonstrate that nucleoside analogues, cornerstones of anticancer and antiviral treatments, also have great potential to be repurposed as antibiotics so that an old drug can learn new tricks.

Fluorescence-based assay for polyprenyl phosphate-GlcNAc-1-phosphate transferase (WecA) and identification of novel antimycobacterial WecA inhibitors

Polyprenyl phosphate-GlcNAc-1-phosphate transferase (WecA) is an essential enzyme for the growth of Mycobacterium tuberculosis (Mtb) and some other bacteria. Mtb WecA catalyzes the transformation from UDP-GlcNAc to decaprenyl-P-P-GlcNAc, the first membrane-anchored glycophospholipid that is responsible for the biosynthesis of mycolylarabinogalactan in Mtb. Inhibition of WecA will block the entire biosynthesis of essential cell wall components of Mtb in both replicating and non-replicating states, making this enzyme a target for development of novel drugs. Here, we report a fluorescence-based method for the assay of WecA using a modified UDP-GlcNAc, UDP-Glucosamine-C6-FITC (1), a membrane fraction prepared from an M. smegmatis strain, and the E. coli B21WecA. Under the optimized conditions, UDP-Glucosamine-C6-FITC (1) can be converted to the corresponding decaprenyl-P-P-Glucosamine-C6-FITC (3) in 61.5% yield. Decaprenyl-P-P-Glucosamine-C6-FITC is readily extracted with n-butanol and can be quantified by ultraviolet-visible (UV-vis) spectrometry. Screening of the compound libraries designed for bacterial phosphotransferases resulted in the discovery of a selective WecA inhibitor, UT-01320 (12) that kills both replicating and non-replicating Mtb at low concentration. UT-01320 (12) also kills the intracellular Mtb in macrophages. We conclude that the WecA assay reported here is amenable to medium- and high-throughput screening, thus facilitating the discovery of novel WecA inhibitors.

Structural insights into inhibition of lipid I production in bacterial cell wall synthesis

Antibiotic-resistant bacterial infection is a serious threat to public health. Peptidoglycan biosynthesis is a well-established target for antibiotic development. MraY (phospho-MurNAc-pentapeptide translocase) catalyzes the first and an essential membrane step of peptidoglycan biosynthesis. It is considered a very promising target for the development of new antibiotics, as many naturally occuring nucleoside inhibitors with antibacterial activity target this enzyme^1-4. However, antibiotics targeting MraY have not been developed for clinical use mainly due to a lack of structural insight into inhibition of this enzyme. Here we present the crystal structure of MraY from Aquifex aeolicus (MraY_AA) in complex with its naturally occurring inhibitor, muraymycin D2 (MD2). Upon binding MD2, MraY_AA undergoes remarkably large conformational rearrangements near the active site, which lead to the formation of a nucleoside-binding pocket and a peptide-binding site. MD2 binds the nucleoside-binding pocket like a two-pronged plug inserting into a socket. Additional interactions it makes in the adjacent peptide-binding site anchor MD2 to and enhance its affinity for MraY_AA. Surprisingly, MD2 does not interact with three acidic residues or the Mg²⁺ cofactor required for catalysis, suggesting that MD2 binds to MraY_AA in a manner that overlaps with, but is distinct from its natural substrate, UDP-MurNAc-pentapeptide. We have deciphered the chemical logic of MD2 binding to MraY_AA, including how it avoids the need for pyrophosphate and sugar moieties, which are essential features for substrate binding. The conformational plasticity of MraY could be the reason that it is the target of many structurally distinct inhibitors. These findings can inform the design of new inhibitors targeting MraY as well as its paralogs, WecA and TarO.

Treatment of Clostridium difficile infection using SQ641, a capuramycin analogue, increases post-treatment survival and improves clinical measures of disease in a murine model

OBJECTIVES

Clostridium difficile infection (CDI) is a primary cause of antibiotic-associated diarrhoeal illness. Current therapies are insufficient as relapse rates following antibiotic treatment range from 25% for initial treatment to 60% for treatment of recurrence. In this study, we looked at the efficacy of SQ641 in a murine model of CDI. SQ641 is an analogue of capuramycin, a naturally occurring nucleoside-based compound produced by Streptomyces griseus.

METHODS

In a series of experiments, C57BL/6 mice were treated with a cocktail of antibiotics and inoculated with C. difficile strain VPI10463. Animals were treated orally with SQ641 for 5 days at a dose range of 0.1-300 mg/kg/day, 20 mg/kg/day vancomycin or drug vehicle. Animals were monitored for disease severity, clostridial shedding and faecal toxin levels for 14 days post-infection.

RESULTS

Five day treatment of CDI with SQ641 resulted in higher 14 day survival rates in mice compared with either vancomycin or vehicle alone. CDI survival rates were 100% (13 of 13) and 94% (32 of 34), respectively, in the 1 and 10 mg/kg/day SQ641 treatment groups, 37% (7 of 19) with vancomycin treatment at 20 mg/kg/day and 32% (14 of 44) in the vehicle-only control group. Secondary measures of efficacy, such as prevention of weight loss, decreased disease severity, decreased C. difficile shedding and decreased toxin in faeces, were observed with SQ641 and vancomycin treatment.

CONCLUSIONS

SQ641 is effective for CDI treatment with prevention of relapse in the murine model of CDI.

The anti-tuberculosis agents under development and the challenges ahead

Tuberculosis (TB) is a serious health problem causing 1.5 million deaths worldwide. After the discovery of first-line anti-TB drugs, the mortality rate declined sharply, however, the emergence of drug-resistant strains and HIV co-infection have led to increased incidence of this disease. A number of new potential antitubercular drug candidates with novel modes of action have entered clinical trials in recent years. Compounds such as gatifloxacin, moxifloxacin and linezolid, the already known antibiotics are currently being evaluated for their anti-TB activity. OPC-67683 and TMC207 have been approved for the treatment of MDR-TB patients recently, while PA-824, SQ109, PNU-100480, AZD5847, LL3858, SQ609, SQ641, BTZ043, DC-159a, CPZEN-45, Q-203, DNB1, TBA-354 are in various phases of clinical and preclinical developments. This review evaluates the current status of TB drug development and future aspects.

Discovery of a capuramycin analog that kills nonreplicating Mycobacterium tuberculosis and its synergistic effects with translocase I inhibitors

Capuramycin (1) and its analogs are strong translocase I (MurX/MraY) inhibitors. In our SAR studies of capuramycin analogs against M. tuberculosis (Mtb), we observed for the first time that a capuramycin analog, UT-01320 (3) killed non-replicating (dormant) Mtb at low concentrations under low-oxygen conditions, whereas selective MurX inhibitors killed only replicating Mtb under aerobic conditions. Interestingly, 3 did not exhibit MurX enzyme inhibitory activity even at high concentrations, however, 3 inhibited bacterial RNA polymerases with the IC₅₀ values of 100-150 nM range. A new RNA polymerase inhibitor 3 displayed strong synergistic effects with a MurX inhibitor SQ 641 (2), a promising preclinical TB drug.

Current status and future trends in the diagnosis and treatment of drug-susceptible and multidrug-resistant tuberculosis

The global burden of tuberculosis (TB) is still large. The increasing incidence of drug-resistant, multidrug-resistant (MDR) (resistant to at least rifampicin and isoniazid), and extensively drug-resistant (XDR) (additionally resistant to a fluoroquinolone and kanamycin/amikacin/capreomycin) strains of Mycobacterium tuberculosis and the association of active disease with human immunodeficiency virus coinfection pose a major threat to TB control efforts. The rapid detection of M. tuberculosis strains and drug susceptibility testing (DST) for anti-TB drugs ensure the provision of effective treatment. Rapid molecular diagnostic and DST methods have been developed recently. Treatment of drug-susceptible TB is effective in ≥95% of disease cases; however, supervised therapy for ≥6 months is challenging. Non-adherence to treatment often results in the evolution of drug-resistant strains of M. tuberculosis due to mutations in the genes encoding drug targets. Sequential accumulation of mutations results in the evolution of MDR and XDR strains of M. tuberculosis. Effective treatment of MDR-TB involves therapy with 5-7 less effective, expensive, and toxic second-line and third-line drugs for ≥24 months and is difficult in most developing countries. XDR-TB is generally an untreatable disease in developing countries. Some currently existing drugs and several new drugs with novel modes of action are in various stages of development to shorten the treatment duration of drug-susceptible TB and to improve the outcome of MDR-TB and XDR-TB.

Therapeutic efficacy of SQ641-NE against Mycobacterium tuberculosis

A phospholipid-based nanoemulsion formulation of SQ641 (SQ641-NE) was active against intracellular Mycobacterium tuberculosis in J774A.1 mouse macrophages, although SQ641 by itself was not. Intravenous (i.v.) SQ641-NE was cleared from circulation and reached peak concentrations in lung and spleen in 1 h. In a murine tuberculosis (TB) model, 8 i.v. doses of SQ641-NE at 100 mg/kg of body weight over 4 weeks caused a 1.73 log10 CFU reduction of M. tuberculosis in spleen and were generally bacteriostatic in lungs.

Improved synthesis of capuramycin and its analogues

Capuramycin and its congeners are considered to be important lead molecules for the development of a new drug for multidrug-resistant (MDR) Mycobacterium tuberculosis infections. Extensive structure-activity relationship studies of capuramycin to improve the efficacy have been limited because of difficulties in selectively chemically modifying the desired position(s) of the natural product with biologically interesting functional groups. We have developed efficient syntheses of capuramycin and its analogues by using new protecting groups, derived from the chiral (chloro-4-methoxyphenyl)(chlorophenyl)methanols, for the uridine ureido nitrogen and primary alcohol. The chiral nonracemic (2,6-dichloro-4-methoxyphenyl)(2,4-dichlorophenyl)methanol derivative is a useful reagent to resolve rac-3-amino-1,3-dihydro-5-phenyl-2H-1,4-benzodiazepin-2-one, the (S)-configuration isomer of which plays a significant role in improving the mycobactericidal activity of capuramycin.

Antimycobacterial drugs currently in Phase II clinical trials and preclinical phase for tuberculosis treatment

INTRODUCTION

In 2010, about 8.8 million new cases of tuberculosis were recorded and 1.1 million people died of tuberculosis worldwide. Although numbers are in decrease since 2006, tuberculosis still represents a global issue and a major public health threat, due to appearance of multidrug-resistant and extensively drug-resistant tuberculosis cases. Although anti-tuberculosis drugs currently used are effective against tuberculosis, they present however more and more limits, especially in treating complex cases of tuberculosis, increasing therefore the need to develop new tools and approaches to treat tuberculosis today.

AREAS COVERED

In this review, we describe anti-tuberculosis drugs in Phase II clinical trials and in preclinical phase that are likely to play a crucial role in the management of tuberculosis cases in a near future. SQ109, TMC207, nitroimidazoles, and oxazolidinones are currently in Phase II clinical trials while BDM31343, SQ641, CPZEN-45, RBx 8700, DC-159a, and BTZ043 are in preclinical phase.

CONCLUSION

These drugs, alone or in different combinations represent a promising future for the treatment of tuberculosis. Continual conjugative efforts between governments and private organizations worldwide are essential for building new strategies for discovery and the development of new anti-tuberculosis drugs.

Treatment and chemoprophylaxis for paratuberculosis

There is no definitive cure for Mycobacterium avium subsp. paratuberculosis (MAP) infections, but several therapeutic agents may be used to alleviate clinical signs of Johne’s disease (JD) in ruminants of significant value. Treatment has to be maintained for the life of the animal and treated animals usually continue to shed MAP. No drugs are approved for treatment of JD in the United States; any drug use is “extra-label.” Isoniazid, rifampin, and clofazimine are most commonly used for treatment. Monensin, may aid in the prevention of infection in calves and to lower MAP fecal shedding in infected adult cattle.

SQ109 and PNU-100480 interact to kill Mycobacterium tuberculosis in vitro

OBJECTIVES

To investigate in vitro interaction between two compounds, SQ109 and PNU-100480, currently in development for the treatment of Mycobacterium tuberculosis (MTB).

METHODS

The two-drug interactions between SQ109 and PNU-100480 and its major metabolite PNU-101603 were assessed by chequerboard titration, and the rate of killing and intracellular activity were determined in both J774A.1 mouse macrophages and whole blood culture.

RESULTS

In chequerboard titration, interactions between SQ109 and either oxazolidinone were additive. In time-kill studies, SQ109 killed MTB faster than PNU compounds, and its rate of killing was further enhanced by both oxazolidinones. The order of efficacy of single compounds against intracellular MTB was SQ109 > PNU-100480 > PNU-101603. At sub-MIC, combinations of SQ109 + PNU compounds showed improved intracellular activity over individual drugs; at ≥MIC, the order of efficacy was SQ109 > SQ109 + PNU-100480 > SQ109 + PNU-101603. In whole blood culture, the combined bactericidal activities of SQ109 and PNU-100480 and its major metabolite against intracellular M. tuberculosis did not differ significantly from the sum of the compounds tested individually.

CONCLUSIONS

SQ109 and PNU combinations were additive and improved the rate of MTB killing over individual drugs. These data suggest that the drugs may work together cooperatively to eliminate MTB in vivo.

Identification of SQ609 as a lead compound from a library of dipiperidines

We recently reported that compounds created around a dipiperidine scaffold demonstrated activity against Mycobacterium tuberculosis (Mtb) (Bogatcheva, E.; Hanrahan, C.; Chen, P.; Gearhart, J.; Sacksteder, K.; Einck, L.; Nacy, C.; Protopopova, M. Bioorg. Med. Chem. Lett.2010, 20, 201). To optimize the dipiperidine compound series and to select a lead compound to advance into preclinical studies, we evaluated the structure-activity relationship (SAR) of our proprietary libraries. The (piperidin-4-ylmethyl)piperidine scaffold was an essential structural element required for antibacterial activity. Based on SAR, we synthesized a focused library of 313 new dipiperidines to delineate additional structural features responsible for antitubercular activity. Thirty new active compounds with MIC 10-20 μg/ml on Mtb were identified, but none was better than the original hits of this series, SQ609, SQ614, and SQ615. In Mtb-infected macrophages in vitro, SQ609 and SQ614 inhibited more than 90% of intracellular bacterial growth at 4 μg/ml; SQ615 was toxic to these cells. In mice infected with Mtb, weight loss was completely prevented by SQ609, but not SQ614, and SQ609 had a prolonged therapeutic effect, extended by 10-15 days, after cessation of therapy. Based on in vitro and in vivo antitubercular activity, SQ609 was identified as the best-in-class dipiperidine compound in the series.