Rifamycin B producer

The specific and proximate precursor of the mCyN unit in ansamycin polyketides is 3-amino-5-hydroxybenzoic acid 59 (AHBA) [94]. The biosynthesis of AHBA has recently been described by Floss and co-workers from the initial branch point of the shikimic acid pathway prior to 3-deoxy-D-flra/jzno-heptulo-sonic acid 7-phosphate (DAHP) [95]. The pathway shown in Scheme 25 was delineated by feedings of the proposed AHBA precursors, in labelled forms, to cell-free extracts of both the rifamycin B producer A. mediterranei S699 and the ansatrienin A producer S. collinus Tul892. In these experiments each of the compounds 61-64 was converted into AHBA with generally increasing efficiency. Most importantly the shikimate pathway compound DAHP cannot replace phosphoenolpyruvate 61 and erythrose 4-phosphate 60, or aminoDAHP 62 as the precursor of AHBA 59. 

The present study reports the first successful long-term cultivation of rifamycin-B producing Nocardia mediterranei and the problems encountered in growing E. coli and k. niger cells in the dual hollow-fiber bioreactor. 

Unusual features in this pattern for rifamycin S biosynthesis are loss of the propionate-derived methyl group from C-28 and insertion of oxygen between C-12 and C-29 of a precursor (195). Important support for the correctness of these conclusions comes from the isolation, from a N. mediterranei mutant, of rifamycin W (196), which possesses the unmodified skeleton (195) and whose biosynthesis accords with that illustrated in (195). " Moreover, rifamycin W (196) was found to be converted by a rifamycin B-producing strain of N. mediterranei into rifamycin B [as (193), with oxygen-substituted hydroquinone ring b], and it may be therefore that rifamycin W is an important intermediate in the biosynthesis of rifamycins. 

Rifamycin B, produced by Amycolatopsis mediterranei, is one of the most notable members of the ansamycin family [36, 37, 64, 65] (Fig. 14). It has been used clinically in a synthetically modified form called rifampicin and it is still one of the first-line therapies effective in the treatment of tuberculosis and other mycobacterial infections. The starter unit for rifamycin polyketide assembly is part of the chromophore and is derived from 3-amino-5-hydroxybenzoic acid. Five polyketide synthases are involved in the formation of rifamycin chromophore and the first polyketide synthase contains at the N terminus the loading domain for 3-amino-5-hydroxybenzoic acid, which consists of an acyl-CoA ligase linked to ACP, and module 1-3. The rifamycin polyketide synthase lacks a TE domain at the C terminus. The release of polyketide chain from polyketide synthase and the formation of amide to generate the macrocyclic lactam will be catalyzed by RifF, which is very similar to arylamine A-acetyltransferase. 

An early aromatic ansamycin-precursor containing the seven-carbon amino starter unit and designated as P8/1-OG (72) was isolated from the non-rifamycin producing UV-mutants derived from the Nocardia mediterranei strain N813 (a rifamycin B producer) [118]. This compound does not possess an ansa moiety, and can be considered to be an early ansamycin-precursor. 

Rifampicin (RIF, Fig. 22.50) is a broad-spectmm semisynthetic derivative of the complex macrocyclic antibiotic rifamycin B, produced by Streptomyces mediterranei, and is known as rifampin outside the UK. An important feature about RIF is that it is active against both actively growing and slowly metabolising non-growing bacilli. The latter feature is thought to be important in reducing the treatment from 12-18 months to 9 months. 

Rifamycins. The rifamycins were first isolated from a broth of Nocardia mediterranei (the producing organism was originally identified as Streptomyces mediterranei). The rifamycins, the stmctures of which are shown in Figure 3, were originally designated as rifomycins. Only rifamycin B (22), which accounts for 10—15% of the cmde complex, can be isolated easily as a stable, crystalline compound (6,89,90). 

The ansamycins (rifamycin B and rifamycin SV) are produced by certain strains of Nocardia mediterranei and act by inhibition of messenger RNA (m-RNA) synthesis, and consequently of bacterial protein synthesis. Structurally, they present a characteristic ansa structure, made of a ring containing a naphthohydroquinone system spanned by an aliphatic chain. The two ansamycins differ in the type of substituent on the... 

Ansamycins are a class of macrocyclic compounds in which non-adjacent positions on an aromatic ring system are spanned by the long aliphatic bridge (Latin ansa = handle). The aromatic portion may be a substituted naphthalene or naphthaquinone, or alternatively a substituted benzene ring. The macrocycle in the ansamycins is closed by an amide rather than an ester linkage, i.e. ansamycins are lactams. The only ansamycins currently used therapeutically are semi-synthetic naphthalene-based macrocycles produced from rifamycin B. 

The rifamycins are ansamycin antibiotics produced by cultures of Amycolatopsis mediterranei (formerly Nocardia mediterranei or Streptomyces mediterranei). The crude antibiotic mixture was found to contain five closely related substances rifamycins A-E, but if the organism was cultured in the presence of sodium diethyl barbiturate (barbitone or barbital), the product was almost entirely rifamycin B (Figure 3.71). Rifamycin B has essentially no antibacterial activity, but on standing in aqueous solution in the presence of air, it is readily transformed by oxidation and intramolecular nucleophilic addition into rifamycin O, which... 

Rifamycin SV is a semi-synthetic antibiotic derived from rifamycin B, a substance produced during growth of certain strains of Streptomyces mediterranei. 

Rifampin is used as an antibiotic. It is a semisynthetic derivative of rifamycin B, a macrocyclic antibiotic produced by the mold Streptomyces mediterranei. 

Rifamycins A to E have been described. From rifamycin B are produced rifamide (rifamycin B diethylamide) and rifamycin SV, which is one of the most useful and least toxic of the rifamycins. 

Only Nocardia mediterranei was grown successfully to make possible long term operation of 50 days or more, producing antibiotics rifamycin B with a volumetric productivity of 125 pg/mL/h based on the volume occupied by the immobilized cells. This corresponds to a 30-fold increase over the productivity of a comparable batch system. 

Manufacture and Processing. Although fermentation procedures have not been reported, assumptions concerning fermentation media and optimal conditions have been made (95,174). The transformation of the biologically inactive rifamycin B to the biologically active rifamycin S is usually accompHshed chemically. Several rifamycin B oxidases have been isolated that can enzymatically transform rifamycin B to rifamycin O, which is hydrolyzed in the fermentation medium to rifamycin S. The enzymes from Monocillium spp. ATC 20621 and Humicola spp. ATCC 20620 are intracellular (175,176) whereas the enzyme from Curvularia lunata var aeri is extracellular (177). The use of a fluidized bed reactor containing immobilized whole cells of Humicola for the transformation of rifamycin B to rifamycin S has been described (178). Rifamycin SV producing strains have been isolated, but it is not known if these strains are used commercially. 

P8/1-OG (72) produced by Nocardia mediterranei P14 is considered an early metabolite of rifamycin B (1). To investigate the origin of the C7N-unit of 72, racemic [l,2- 3C2]glycerol was administered to growing cultures of Nocardia mediterranei P14 and the C-NMR spectrum of labeled P8/1-OG (72) was studied [195]. Two incorporation patterns of racemic [l,2- C2]glycerol were considered possible (Fig. 7). 

On the other hand, the damavaricins are regarded as precursors of the streptovaricins [86], protorifamycin I (34), which is structurally related to the protostreptovaricins, and to rifamycin W (20) [83]. Washed mycelium of a rifamycin B (1) producing Nocardia mediterranei transformed C-rifamycin W (20) into C-rifamycin B (1). Consequently, it was suggested that rifamycin W (20) was the normal precursor of other rifamycins [75]. 

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