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At least 19 recordsLinked to original sources
PubMed1982

Oxygen Enhancement of bactericidal activity of rifamycin SV on Escherichia coli and aerobic oxidation of rifamycin SV to rifamycin S catalyzed by manganous ions: the role of superoxide.

Oxygen enhanced the bactericidal activity of rifamycin SV to Escherichia coli K12. Anaerobically grown cells, which had a low level of superoxide dismutase, were more susceptible to the bactericidal activity than aerobically grown cells, which contained a high level of superoxide dismutase. Oxygen also enhanced the inhibition of RNA polymerase activity of rifamycin SV, when Mn2+ was used as a cofactor. Rifamycin S was reduced to rifamycin SV by NADPH catalyzed by cell-free extracts of Escherichia coli K12. These results indicate that the inhibition of bacterial growth by rifamycin SV is due to the production of active species of oxygen resulting from the oxidation-reduction cycle of rifamycin SV in the cells. The aerobic oxidation of rifamycin SV to rifamycin S was induced by metal ions, such as Mn2+, Cu2+, and Co2+. The most effective metal ion was Mn2+. In the presence of Mn2+, accompanying the consumption of 1 mol of oxygen and the oxidation of 1 mol of rifamycin SV, 1 mol of hydrogen peroxide and 1 mol of rifamycin S were formed. Superoxide was generated during the autoxidation of rifamycin SV. Superoxide dismutase inhibited the formation of rifamycin S, but scavengers for hydrogen peroxide and the hydroxyl radical did not affect the oxidation. A mechanism of Mn2+-catalyzed oxidation of rifamycin SV is proposed and its relation to bactericidal activity is discussed.

Aerobiosis↗
PubMed2002

New insights into rifamycin B biosynthesis: isolation of proansamycin B and 34a-deoxy-rifamycin W as early macrocyclic intermediates indicating two separated biosynthetic pathways.

Proansamycin B, the formerly postulated intermediate of rifamycin B biosynthesis, was isolated from cultures of the Amycolatopsis mediterranei mutant F1/24. The structure was determined using UV, IR, NMR and MS techniques. Biotransformation studies demonstrate that proansamycin B is an intermediate of a shunt pathway, a 8-deoxy variant, of rifamycin B biosynthesis leading to 8-deoxy-rifamycin B as the final product. In addition, 34a-deoxy-rifamycin W, the direct precursor of rifamycin W, could be isolated representing the earliest macrocyclic intermediate obtained so far in the biosynthetic route to rifamycin B. Furthermore, the new rifamycin W-28-desmethyl-28-carboxy and rifamycin W-hemiacetal, intermediates in the transformation sequence of rifamycin W to rifamycin S, were isolated. Application of proton NMR measurements (double resonance and ROESY experiments) on the latter compound indicated that the stereochemistry at the chiral center C-28 is R.

Actinomycetales↗
PubMed1998

Comprehensive study on structure-activity relationships of rifamycins: discussion of molecular and crystal structure and spectroscopic and thermochemical properties of rifamycin O.

The mechanism of action of rifamycins against bacterial DNA-dependent RNA polymerase has been explained on the basis of the spatial arrangement of four oxygens which can form hydrogen bonds with the enzyme. Structural descriptors are derived from X-ray diffraction crystal structures of 25 active and nonactive rifamycins. Principal component analysis is used to find the combination of structural parameters which better discriminate between active and nonactive rifamycins. Two possible mechanisms of molecular rearrangement are described which can convert nonactive into active conformations. The energy involved for conformational rearrangements is studied by molecular modeling techniques. Methyl C34 is found to play a key role for determining the geometry of the pharmacophore. Rifamycin O, reported to be active, is obtained by oxidation of rifamycin B and is studied by X-ray single-crystal diffractometry, by solution IR and NMR spectroscopy, and by thermal analysis. Surprisingly the oxidation process is totally stereospecific, and an explanation is given based on solution spectroscopic evidence. The conformation found in the solid state is typical of nonactive compounds, and molecular mechanics calculations show that a molecular rearrangement to the active conformation would require about 15 kcal/mol. Thermal analysis confirms that rifamycin O has a sterically constrained conformation. Therefore, it is likely that the antibiotic activity of rifamycin O is due either to chemical modification prior to reaching the enzyme or to conformational activation.

Calorimetry, Differential Scanning↗
PubMed1982

Transformation of rifamycin S into rifamycins B and L. A revision of the current biosynthetic hypothesis.

The transformation of rifamycin S into rifamycins B and L was reinvestigated in order to establish more detailed pathways. Our results exclude rifamycin O as a common progenitor in the biosyntheses of rifamycins B and L. Rifamycins B and L are formed from rifamycin S (SV) by different pathways using different C3-precursors for the biosynthesis of their glycolic acid moieties. A thiamine-dependent enzyme (decarboxylase) seems to be involved in the transformation reaction.

Acremonium↗
PubMed1982

Aerobic oxidation of rifamycin SV to rifamycin S catalyzed by horseradish peroxidase.

The aerobic oxidation of rifamycin SV to rifamycin S was catalyzed by horseradish peroxidase. The oxidation rate increased with increasing pH. The oxidation was inhibited by catalase, but superoxide dismutase enhanced the oxidation rate of rifamycin SV. Superoxide inhibited the oxidation and superoxide dismutase relieved the inhibition of oxidation by superoxide. An oxidation mechanism of rifamycin SV catalyzed by horseradish peroxidase which accounts for these data is proposed and a convenient positive assay for superoxide dismutase, using the rifamycin SV-horseradish peroxidase-O2 system, is described.

Aerobiosis↗
PubMed2006

In vitro activity of novel rifamycins against rifamycin-resistant Staphylococcus aureus.

We describe novel rifamycin derivatives (new chemical entities [NCEs]) that retain significant activity against a comprehensive collection of Staphylococcus aureus strains that are resistant to rifamycins. This collection of resistant strains contains 21 of the 26 known single-amino-acid alterations in RpoB, the target of rifamycins. Some NCEs also demonstrated a lower frequency of resistance development than rifampin and rifalazil in S. aureus as measured in a resistance emergence test. When assayed for activity against the strongest rifamycin-resistant mutants, several NCEs had MICs of 2 microg/ml, in contrast to MICs of rifampin and rifalazil, which were 512 microg/ml for the same strains. The properties of these NCEs therefore demonstrate a significant improvement over those of earlier rifamycins, which have been limited primarily to combination therapy due to resistance development, and suggest a potential use of these NCEs for monotherapy in several clinical indications.

Drug Resistance, Bacterial↗
PubMed1995

Enantiomeric resolution using the macrocyclic antibiotics rifamycin B and rifamycin SV as chiral selectors for capillary electrophoresis.

Rifamycin B and rifamycin SV belong to the class of macrocyclic antibiotics known as ansamycins. These macrocyclic antibiotics were used as chiral selectors in capillary electrophoresis to enantioselectively resolve a number of chiral compounds. They contain groups capable of providing the types of multiple interactions necessary to achieve chiral recognition between enantiomers. In fact, they appear to be complimentary in the types of compounds they can enantiomerically resolve. Rifamycin B is shown to be enantioselective towards positively charged compounds, while rifamycin SV was enantioselective towards negatively charged solutes. The choice of wavelength for detection significantly affects sensitivity. Monitoring one of the wavelengths which coincide with the absorption minima of the chiral selector enhances sensitivity. Resolution is enhanced by keeping the amount of analyte injected on column as low as possible and it is demonstrated that it is possible to detect as little as 0.1% of one enantiomer in the presence of the other enantiomer using indirect detection.

Anti-Bacterial Agents↗
PubMed1978

A genetic approach to the biosynthesis of the rifamycin-chromophore in Nocardia mediterranei. I. Isolation and characterization of a pentose-excreting auxotrophic mutant of Nocardia mediterranei with drastically reduced rifamycin production.

The mutant under study, designated A8, is derived from a Nocardia mediterranei strain, N813, which is a high rifamycin B producer. A8 is auxotrophic for aromatic amino acids and produces much less rifamycin B than the parent. A mixture of pentoses with D (--) ribulose as the main product is accumulated in the fermentation broth of this mutant. It was shown to be affected in its transketolase activity as no formation of D-sedoheptulose -7P from pentose-phosphates could be detected in vitro using crude extracts. The only pathway so far known which is derived from D-sedoheptulose-7P is the shikimate pathway leading to aromatic amino acids and vitamins. Biochemical and genetic investigations with mutant A8, which is defective in both the biosynthesis of rifamycins and the biosynthesis of shikimate pathway products, show that the seven-carbon amino unit of the rifamycin-chromophore must be derived from an intermediate of the shikimate pathway.

Culture Media↗
PubMed1978

A genetic approach to the biosynthesis of the rifamycin-chromophore in Nocardia mediterranei. II. Isolation and characterization of a shikimate excreting auxotrophic mutant of Nocardia mediterranei with normal rifamycin-production.

The mutant under study, designated A10, is derived from a Nocardia mediterranei strain, N813, which is a high rifamycin B producer. A10 is auxotrophic for aromatic amino acids but unlike A8 (see preceding paper) produces the same amount of rifamycin B as the parent. Shikimic acid and 3-dehydroshikimic acid are accumulated in the fermentation broth of this mutant. It was shown to be blocked in one of the enzymes leading from shikimate to chorismate. No formation of shikimate-3-phosphate from shikimate and ATP could be detected in vitro using crude extracts of this mutant and of the parent. As mutant A10 is only defective in the biosynthesis of aromatic amino acids and not in the biosynthesis of rifamycins it would appear that the seven-carbon amino unit of the rifamycin-chromophore must be derived from an intermediate of the shikimate pathway not behind shikimate. By referring to the results of the preceding paper it can be seen that the origin of this moiety can definitely be localized between 3-deoxy-D-arabinoheptulosonic acid-7-phosphate and shikimate.

Culture Media↗
PubMed1985

Absence from sera from normal individuals or from rifampin-treated leprosy patients (THELEP trials) of antibody to rifamycin-protein or rifamycin-membrane conjugates.

It has been reported that normal individuals have precipitating antibody which binds to rifamycin-conjugated proteins. An enzyme-linked immunosorbent assay has failed to confirm this claim, although antibodies demonstrable in a solid-phase binding assay are easily raised in mice if complete adjuvant is used. Moreover, no antibodies to rifamycin-protein conjugates were found in sera from the patients included in THELEP trials of six rifampin-containing regimens. Similarly, there was no antibody by the indirect Coombs test performed in another laboratory. Further studies using rifamycin-membrane conjugates regarded as more likely to be immunogenic in vivo also failed to reveal antibody in patients' sera, although this technique revealed an interesting antibody in one of four control sera known to be positive by the indirect Coombs test.

Animals↗
PubMed2004

Risk factors for relapse and acquired rifamycin resistance after directly observed tuberculosis treatment: a comparison by HIV serostatus and rifamycin use.

We sought to determine the risk of acquired rifamycin resistant (ARR) tuberculosis associated with rifampin- versus rifabutin-based directly observed therapy and to assess the risk factors for relapse of tuberculosis. This observational cohort study included patients with culture-confirmed rifamycin-susceptible tuberculosis reported to the Baltimore City Health Department (Baltimore, MD) during the period of January 1993 through December 2001. Of the 407 patients, 108 (27%) were human immunodeficiency virus (HIV) seropositive, 161 (40%) were HIV seronegative, and 138 (34%) had an unknown serostatus. Three (2.8%) of 108 HIV-seropositive persons had ARR tuberculosis, compared with 0 of 299 persons with negative or unknown HIV serostatus (P=.02). Among HIV-seropositive patients, 3 (3.7%) of 81 who were treated with rifampin and 0 of 27 who were treated with rifabutin had ARR tuberculosis (P=.57). Among HIV-seropositive patients, the only risk factor for recurrent tuberculosis was a low median initial CD4+ T lymphocyte count (51 vs. 138 cells/mm3; P=.02). The median CD4+ T lymphocyte count among patients with ARR tuberculosis was 51 cells/mm3. ARR tuberculosis can occur with rifampin-based regimens, but in this study, the risk was not significantly higher than that for a rifabutin-based regimen.

Adult↗
PubMed1980

Biological activity of a new class of rifamycins. Spiro-piperidyl-rifamycins.

The biological properties of spiro-piperidyl-rifamycins, a new class of rifamycin antibiotics, are described. In these derivatives the positions 3 and 4 have been incorporated into an imidazolyl ring bearing a spiro-piperidyl group N substituted with linear and branched aliphatic chains. The in vitro antibacterial activity against Staphylococcus aureus and Mycobacterium tuberculosis increases with the number of the carbon atoms in the linera side chain, whereas the inhibitory effect on Escherichia coli is lowered. The antibacterial activity is only marginally affected by branching of the side chain. In vivo (experimental infections of mice) the optimal therapeutic activity against M. tuberculosis is shown by compounds bearing 3 approximately 5 carbon atoms as a linear or branched side chain; in comparison with rifampicin, the potency of these derivatives is 2 approximately 3 times higher. The finding is in a good agreement with the exceptional tissue tropism, which seems to be a favourable property of this group of derivatives.

Animals↗
PubMed2002

Acquired rifamycin resistance in persons with advanced HIV disease being treated for active tuberculosis with intermittent rifamycin-based regimens.

Rifamycin drugs (i.e., rifampin, rifabutin, and rifapentine) are essential for short-course chemotherapy in persons with active tuberculosis (TB). However, adverse drug-drug interactions complicate the concurrent use of rifamycins and protease inhibitor drugs in persons with active TB who also are infected with human immunodeficiency virus (HIV-TB). CDC has recommended use of rifabutin in place of rifampin in multidrug regimens for the treatment of active TB in HIV-TB because rifabutin can be administered with antiretroviral treatment regimens that include protease inhibitors (1,2). These recommendations included twice-weekly intermittent therapy. Because intermittent rifabutin-based regimens had not been evaluated in clinical trials of HIV-TB, CDC's TB Trials Consortium (TBTC) initiated TBTC Study 23, a single-arm trial of twice-weekly rifabutin-based therapy for treatment of HIV-TB.

AIDS-Related Opportunistic Infections↗
PubMed2005

Expeditious asymmetric synthesis of a stereoheptad corresponding to the C(19)-C(27)-ansa chain of rifamycins: formal total synthesis of Rifamycin S.

In the presence of sulfur dioxide and an acid promoter, (-)-(1E,3Z)-2-methyl-1-((1S)-1-phenylethoxy)penta-1,3-dien-3-yl isobutyrate reacts with (Z)-3-(trimethylsilyloxy)pent-2-ene giving a silyl sulfinate intermediate that undergoes, in the presence of palladium catalyst, a desilylation and retro-ene elimination of SO(2) with formation of (-)-(1Z,2S,3R,4S)-1-ethylidene-2,4-dimethyl-5-oxo-3-((1S)-1-phenylethoxy)-heptyl isobutyrate as major product. This ethyl ketone undergoes cross-aldol reaction with (2S)-2-methyl-3-[(tert-butyldimethylsilyl)oxy]propanal giving an aldol that is reduced into a stereoheptad corresponding to the C(19)-C(27)-segment of Rifamycins with high diastereoselectivity and enantiomeric excess.

Catalysis↗
PubMed1985

4-Deoxypyrido[1',2':1,2]imidazo[5,4-c]rifamycin SV derivatives. A new series of semisynthetic rifamycins with high antibacterial activity and low gastroenteric absorption.

A series of 4-deoxypyrido[1',2':1,2]imidazo[5,4-c]rifamycin SV derivatives (6-11) were prepared that demonstrated high antibacterial activity suitable for an intestinal disinfectant. These compounds are zwitterionic in nature and are poorly absorbed through the gastroenteric tract but maintain the ability to cross the bacterial cell wall. X-ray crystallographic data are presented to demonstrate the zwitterionic nature of these compounds. The structure-activity relationship of this novel series of antibiotics is discussed and the derivative with the highest ratio between subcutaneous and oral activity (6) was selected for clinical development. At the outset of this work several 3-(quaternary ammonium bromides) (1-5) were prepared and tested for antibacterial activity. These compounds were demonstrated to be too polar to even cross the bacterial cell wall but led to the synthesis of 6-11.

Animals↗
PubMed2006

Efficacy of novel rifamycin derivatives against rifamycin-sensitive and -resistant Staphylococcus aureus isolates in murine models of infection.

Novel rifamycins (new chemical entities [NCEs]) having MICs of 0.002 to 0.03 microg/ml against Staphylococcus aureus and retaining some activity against rifampin-resistant mutants were tested for in vivo efficacy against susceptible and rifampin-resistant strains of S. aureus. Rifalazil and rifampin had a 50% effective dose (ED50) of 0.06 mg/kg of body weight when administered as a single intravenous (i.v.) dose in a murine septicemia model against a susceptible strain of S. aureus. The majority of NCEs showed efficacy at a lower i.v. dose (0.003 to 0.06 mg/kg). In addition, half of the NCEs tested for oral efficacy had ED50s in the range of 0.015 to 0.13 mg/kg, i.e., lower or equivalent to the oral ED50s of rifampin and rifalazil. NCEs were also tested in the septicemia model against a rifampin-resistant strain of S. aureus. Twenty-four of 169 NCEs were efficacious when administered as a single oral dose of 80 mg/kg. These NCEs were examined in the murine thigh infection model against a susceptible strain of S. aureus. Several NCEs dosed by intraperitoneal injection at 0.06 mg/kg caused a significant difference in bacterial titer compared with placebo-treated animals. No NCEs showed efficacy in the thigh model against a highly rifampin-resistant strain. However, several NCEs showed an effect when tested against a partially rifampin-resistant strain. The NCEs having a 25-hydroxyl moiety were more effective as a group than their 25-O-acetyl counterparts. These model systems defined candidate NCEs as components of potential combination therapies to treat systemic infections or as monotherapeutic agents for topical applications.

Administration, Oral↗