Incorporation into erythromycin

Until recently little was known about the biosynthesis of er3d hromycin from large precursors. A new concept has arisen from the work of Hung and his colleagues (1965) on the role of erythronohde B in the biosynthesis of the antibiotic. When erythronohde B was added to the fermentation in the presence of propionic-l- C acid, unlabelled erythromycins could be isolated. Futhermore, erythronolide- C was efficiently incorporated into erythromycins A, B, and C. These observations, which were supported by kinetic studies, proved that there was a precursor-product relationship between erythronohde B and the erythromycins. Since erythromycin B was poorly converted to erythromycin A, the authors assume that the introduction of an hydroxyl group at C-12 occurred before the glycosidation reaction (Fig. 10). 

Erythromycin, a macrolide antibiotic, lacks a significant chromophore. Detection sensitivity was enhanced by using a wavelength of 200 nm and selecting an injection solvent of lower conductivity than the BGE. In order to facilitate the separation of erythromycin and its related substances, 35% (v/v) ethanol was incorporated into a 150 mM phosphate buffer pH 7.5. Resolution of all of the compounds was achieved in approximately 45 min. The method was employed as an assay method for erythromycin and for impurity determination. Peptide antibiotics, such as colistin and polymyxin, are mixtures of many closely related compounds. A validated CZE method for impurity analysis of polymyxin B was described, employing 130 mM triethanolamine-phosphate buffer at pH 2.5 to reduce the adsorption of analyte onto the capillary wall. Methyl-/l-cyclodextrin (M-/1-CD) and 2-propanol were found to be necessary for selectivity enhancement. Using similar buffer additives, the same group developed and validated a method for colistin analysis. ... 

Azithromycin is an azalide antibiotic, a sub-class of the macrolides. Azithromycin differs chemically from erythromycin in that a methyl substituted nitrogen atom is incorporated into the lactone ring. 

A variety of complex natural compounds are synthesized by using monosaccharides as chiral starting materials. Exemplifying eight representative natural products, i. e., erythromycins, elaiophilin, herbimaycins, calbistrin A, lactacystin, tautomycin, FK-506, and halichondrin B, the methodology how monosaccharides are incorporated into natural product synthesis as chiral pools is described. 

Other antimicrobial agents that have been incorporated into PMMA beads and shown to have useful elution profiles include penicillin G (ben-zylpenicillin), ampicillin, amoxicillin, flucloxacillin, amoxiciUin-clavulanate, cefamandole, cefazolin, tobramycin, netilmicin, imipenem, erythromycin, ciprofloxacin, trimethoprim-sulfamethoxazole, chloramphenicol and vancomycin (Ethell et al 2000, Mader et al 1997, Veyries et al 2000). 

While some success has been reported in analogous studies with polyketide assembly intermediates in Streptomyces metabolites, e.g. erythromycin [41] and tylosin [42], similar experiments on fungal polyketides have been more limited. The di- and tetraketide intermediates (44) and (45), variously doubly labelled with and as indicated in Scheme 14, have been incorporated into de-hydro curvular in (46) by cultures of Alternaria cineriae [43]. However, in contrast to the ease of incorporation of assembly intermediates into aspyrone by A. melleus, the experiments in A. cineriae required considerable experimentation to optimise the feeding conditions and the use of the jS-oxidation inhibitors. The initial experiments [43] depended on the use of UV mutants of A. cineriae which had lost the ability to utilise fatty acids and therefore to degrade the fatty... 

Cane, D. E., and Yang, C.-C. (1987). Macrolide biosynthesis. 4. Intact incorporation of a chain-elongation intermediate into erythromycin. J. Am. Chem. Soc. 109,1255-1257. 

Acetate simultaneously labeled in the methyl group with three deuterium atoms and a was incorporated into terrein. From the spectrum of the metabolite, it was clear that three deuterium atoms were present in the starter methyl group. This result demonstrated that acetate served as a starter acid in terrein biosynthesis (Figure 2.2) [1]. The A-acetylcysteamine thioester (SNAC) and the diketide intermediate of erythromycin A were labeled simultaneously with H and labels. The intact incorporation of the labeled SNAC and diketide intermediate into erythromycin B demonstrated that SNAC was not oxidized to the p-keto thioester before incorporation (Section 7.6) (Figure 2.3) [2]. 

Figure 2.3 Incorporation of a diketide intermediate into erythromycin A.

Fig. 6.1 Structure of the macrolide antibiotic erythromycin (a) which contains a 14-membeied lactone ring. The azalide, azithromycin (b), derived from erythromycin, has an iV-methyl group incorporated into the lactone ring, making it a 15-membered ring (compare highlighted sections)...

When erythromycin is formed in the presence of [i-iO]acetate or [i-i C]-propionate the labelled carbon is incorporated into the erythronohde portion of the molecule but not into either of the sugars, cladinose and desosamine, to which this portion is linked . Different types of biosynthetic pathway are thus involved in the formation of the sugars and of the lactone ring. [i C]Propionate is incorporated into the lactone ring as an intact unit . 

The objectives of this study were to expand the work reported by us in the area of antibiotic-containing hydrogels, and to evaluate the novel chitosan-based functional drug-delivery systems which can be successfully incorporated into dual action bioactive restorative materials containing common antibiotics such as erythromycin, krill oil, aloe and aspirin as commonly used antioxidant species (Figure 11.16). 

Pathways 3 and 4 may be excluded because of the low incorporation of pyruvic-l- C acid into erythromycin (Van k et aL, 1958b). Similarly, Butte and Corcoran (1963), when studying the distribution of the activity originating from the specifically labelled glucoses into the erythronolide, concluded that only a small part of the propionate comes from succinate. The results obtained by Kaneda and his co-workers (1962) from experiments with labelled succinate suggest the incorporation of succinate as an intact unit so that its participation as an intermediate in synthesis of the C3 units cannot be simply ignored. 

Kaneda, T., and J. W. Corcoran a-Methylmalonate incorporation into the branched chain lactone in erythromycin. Federation Proc. 20, 273 (1961). 

Cane has demonstrated that advanced di-, tri- and tetraketide fatty acid precursors are incorporated directly into the nargeiucins, and has noted that an early intermediate in the nargenicin pathway is common to the biosynthetic scheme leading to erythromycin A and... 

The paradigm for both modular PKSs and NRPSs is that each module incorporates one building block into the natural product (Figures 1 and 2). Within each module there are different domains and each domain catalyzes a specific reaction in the assembly of the metabolic product. Model examples of this colinearity between module and domain organization and metabolite structure for type I modular PKS and NRPS systems are respectively represented by erythromycin and tyrocidine biosyntheses. This colinearity is an important feature that underpins our ability to predict structural features of the metabolic products of novel modular PKS and NRPS systems discovered by genomics. 

In addition to the contribution derived from protein-protein interactions, modular recognition and discrimination of incoming substrates also plays a role in controlling the specificity of PKSs, as determined in the DEBS system. The KS domains of DEBS modules 2-6 were shown to have surprising tolerance in vivo to a series of substrates fed diffusively, and were able to incorporate these substrates into novel 6dEB or erythromycin derivatives [59]. In vitro studies on the KS domain of DEBS module 2 likewise showed this domain to be tolerant to a broad range of substrates [60]. Nevertheless, the DEBS modules do not accept all substrates. In vitro studies of module 2, module 3, module 5, and module 6 for acceptance of various diketide substrates showed that all four modules have similar substrate preference, and while all diketide compounds with sy stereochemistry across the a- and /9-posi-tions were accepted by the modules, those compounds with anti stereochemistry were not accepted. It is particularly interesting that all four DEBS modules have similar substrate specificity, despite the fact that their natural substrates differ widely [61]. 

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