Of erythromycin

Many natural products are lactones and it is not unusual to find examples m which the ring size is rather large A few naturally occurring lactones are shown m Figure 19 8 The macrohde antibiotics of which erythromycin is one example are macrocychc (large ring) lactones The lactone ring of erythromycin is 14 membered... 

Erythromycins. Erythromycin A (14, R = OH, R = CH3, R" = H), the most widely used macroHde antibiotic, was the principal product found in culture broths of Streptomjces eTythreus (39), now reclassified as Saccharopoljspora eythraea (40). It contains a highly substituted aglycone, erythronoHde A, (16, R = R = OH) to which desosamine (1, R = OH, R = H) and cladinose (8, R = CH ) are attached (41). The complete stereochemistry of erythromycin A was estabUshed by x-ray analysis of its hydroiodide dihydrate (42) total synthesis of erythromycin A was a landmark achievement (43), a task previously considered hopeless (44). 

Chemical degradation of erythromycin A yielded its aglycone, erythronoHde A (16, R = R = OH), whereas erythronoHde B (16, R = H, R = OH) was obtained from fermentation (63,64). Biosynthesis of erythromycin proceeds via 6-deoxyerythronoHde B (16, R = R = H) and then erythronoHde B (64,65). The first total synthesis of erythromycin-related compounds was erythronoHde B (66) syntheses of erythronoHde A and 6-deoxyerythronoHde B soon foUowed (67,68). 

The acid-instabihty of erythromycin makes it susceptible to degradation in the stomach to intramolecular cyclization products lacking antimicrobial activity. Relatively water-insoluble, acid-stable salts, esters, and/or formulations have therefore been employed to protect erythromycin during passage through the stomach, to increase oral bioavakabihty, and to decrease the variabiUty of oral absorption. These various derivatives and formulations also mask the very bitter taste of macroHdes. 

Another successhil strategy for derivatization of erythromycin employed modification of functional groups involved in intramolecular cyclizations. The C-9 ketone, C-6 hydroxyl group, C-8 proton, and/or C-ll,12-diol of erythromycin were converted into functional groups which participate poorly, if at all, in intramolecular cyclizations. Some derivatives which have been extensively evaluated in preclinical and clinical trials exhibit such desirable properties as better stabiUty under acidic conditions, greater oral bioavadabihty, and higher and more prolonged concentrations of antibiotic in semm and tissues. 

The 11,12-carbonate of erythromycin (32) is an older cycHc ester which had greater stabdity and antibiotic activity by diminishing formation of intramolecular enol ether (27) (136,137). A later analogue, the ll-A/-12-0-cychc carbamate of... 

Other approaches to inhibiting intramolecular cycli2ations of erythromycin have also proven successhil. Erom a series of O-alkyl derivatives of erythromycin, clarithromycin (6-0-methylerythromycin) (37) was selected for clinical development (146,147). Another approach replaced the C-8 proton of erythromycin with duorine, which was accompHshed by both chemical and bioconversion methods to yield durithromycin (38) (148). 

Other macrohdes have been prepared which represent hybrids of stmctures within the 14-membered family, within the 16-membered family, or between the two families. These hybrids have been made by chemical, bioconversion, or genetic manipulations. The 9-0-[(2-methoxyethoxy)methyl]oxime of tylosin (Table 7) was synthesized, using the oxime found in roxithromycin (33) (369). 3-0-Cladinosyl derivatives of 16-membered macrohdes were synthesized in which the neutral sugar of erythromycin (Table 3) was attached to tylosin derivatives at thek 3-hydroxyl group, analogous to its position in erythromycin... 

The University of Idaho and USFWS, with funds from the Bonneville Power Administration, are also gathering data for registration of erythromycin. Erythromycin is intended for control of bacterial kidney disease in salmonid fingerlings that can also be transmitted by broodstock to the eggs (9). If research is completed on schedule and data indicate that the compound is safe and effective, registration is scheduled for 1994 (see Antibiotics, MACROLIDES). 

Branched-chain sugars are found in nature, eg, cladinose, ie, 2,6-dideoxy-3-C-meth5l-3-0-methyl-L- 7 (9hexose [3758-45-0] a component of erythromycin. 

The 2-chlorobenzyl group has been used in the protection of an oxime during the modification of erythromycin K ... 

The culture broth is sterilized by heating it under pressure at about 120°C for about 30 minutes. The broth is cooled and the above inoculant culture is added aseptically. The organism is grown in the broth for 4 days at a temperature of 26°C. During the growth period the broth is stirred and sterile air is blown through the broth at a rate of about 0.5 volume of air per volume of broth per minute. At the end of the growth period the broth shows an antibiotic activity equivalent to about 150 meg of erythromycin per ml of broth. 

The alkaline solution is concentrated in vacuo to a volume of about 30 gallons and the solution is then adjusted to pH 9.5 by the addition of aqueous sodium hydroxide and is allowed to stand. Erythromycin separates as a crystalline material. The crystals are filtered off, the mother liquor is adjusted to about pH 8 by the addition of dilute sulfuric acid and is concentrated in vacuo to a volume of about 30 gallons. The solution is adjusted to about pH 9.5 and allowed to stand, whereupon an additional amount of erythromycin separates in crystalline form. The total amount of erythromycin obtained is about 256 grams. The erythromycin is purified by several recrystallizations from aqueous acetone (2 1 mixture), according to U.S. Patent 2,653,899. 

A solution of 10 grams of d-glucoheptonic acid lactone in 50 ml of distilled water is warmed on a steam bath for about 2 hours to hydrolyze the lactone to the acid. The mixture is cooled and 100 ml of 95% ethanol are added. To the solution of glucoheptonic acid are added about 37 grams of erythromycin and the volume of the reaction mixture is brought to 200 ml by the addition of 95% ethanol. The reaction mixture is stirred for about 2 hours and is filtered through a porcelain filter candle of porosity 02. To provide a steriie product, aseptic technique is used throughout the remainder of the procedure. 

To the fiitered solution are added slowly and with stirring about 1,200 ml of anhydrous ether, to cause precipitation of erythromycin d-glucoheptonate and to keep In solution any excess of unreacted erythromycin. The precipitated erythromycin salt is removed by filtration through a sintered glass funnel, is washed with anhydrous ether and is dried in vacuo. Erythromycin d-glucoheptonate melts over a range of about 95° to 140°C. 

Erylhronoljde B is the biological precursor of erythromycin, a broad-spectrum antibiotic. How many chirality centers does erythronolide B have ... 

Lower stereoselectivities arise, however, from the addition of ester enolates to this glyceralde-hyde4. Another highly stereoselective addition is in the synthesis of erythromycin A where a single product results from the addition of lithiated tert-butyl thiopropanoate to the enantiomerically pure aldehyde (2/ ,3/ ,4,S, 6/ ,7/ ,8,S, 9/ ,10.S, 11 / )-7-acetoxy-3,4 9,10-bis(isopropy1-idenedioxy)-11-methoxymethoxy-2,4,6,8,10-pentamethyltridecanal5. 

Another group of antibiotics that can be inactivated by hydrolysis are 14- and 15- membered macrolides [2]. Esterases cleave the lactone ring. The plasmid encoded ere genes are found in members of the Enter-obacteriaceae and increase the intrinsic resistance. Furthermore, these esterases can also be found in some isolates of erythromycin resistant staphylococci. 

Sabath, L.D. Gersteln, D.A. and Finland, M. "Serum Glutamlc-Oxalacetlc Transaminase. False Elevations During Administration of Erythromycin". New Engl. J. Med. (1968), 279, 1137-1139. 

Fig. 5.11 Erythromycins erythromycin is a mixture of macrolide antibiotics consisting largely of erythromycin A.

Noguchi N, A Emura, H Matsuyama, K O Hara, M Sasatsu, M Kono (1995) Nucleotide sequence and characterization of erythromycin resistance determinant that encodes macrolide 2 phosphotransferas I in Escherichia coli. Antimicrob Agents Chemother 39 2359-2363. 

Kawasaki et /. (1996) have used a supported membrane catalyst for extraction of erythromycin from its dilute, slightly alkaline aqueous solutions. 1-Decanol was used as an intermediate fluid membrane phase and a buffered acidic aqueous solution was used to strip the organic membrane. 

Exchanges between pharmacopoeias are co-ordinated by the Pharmacopoeial Discussion Group (PDG) (International Harmonisation 1995) and it is frequent that one pharmacopoeia participates in a collaborative study organized by another pharmacopoeia, or that several pharmacopoeias share the same batch of reference substance to be used in their respective monographs nevertheless, in this case the reference substance can not be considered as harmonized. A new batch of erythromycin was shared between the United States Pharmacopoeia and the European Pharmacopoeia and was established in a common coEaborative study both for the microbiological assay (used in the USP for formulations) and the liquid chromatographic assay (used in the Ph. Eur. and USP for bulk material). 

Antibiotics may be classified by chemical structure. Erythromycin, chloramphenicol, ampicillin, cefpodoxime proxetil, and doxycycline hydrochloride are antibiotics whose primary structures differ from each other (Fig. 19). Figure 20 shows potential oscillation across the octanol membrane in the presence of erythromycin at various concentrations [23]. Due to the low solubility of antibiotics in water, 1% ethanol was added to phase wl in all cases. Antibiotics were noted to shift iiB,sDS lo more positive values. Other potentials were virtually unaffected by the antibiotics. On oscillatory and induction periods, there were antibiotic effects but reproducibility was poor. Detailed study was then made of iiB,sDS- Figure 21 (a)-(d) shows potential oscillation in the presence of chloramphenicol, ampicillin, cefpodoxime proxetil, and doxycycline hydrochloride [21,23]. Fb.sds differed according to the antibiotic in phase wl and shifted to more positive values with concentration. No clear relationship between activity and oscillation mode due to complexity of the antibacterium mechanism could be discovered but at least it was shown possible to recognize or determine antibiotics based on potential oscillation measurement. 

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