Structure Elucidation of Macrolide Antibiotics Using MSn Analysis and Deuterium Labelling.

The 14- and 16-membered macrolide antibiotics are an important structural class. Ubiquitously produced by a number of bacterial strains, namely actinomycetes, purification and structure elucidation of the wide array of analogs is challenging, both for discovery efforts and methodologies to monitor for byproducts, metabolites, and contaminants. Collision-induced dissociation mass spectrometry offers an attractive solution, enabling characterization of mixtures, and providing a wealth of structural information. However, interpretation of these spectra can be difficult. We present a study of 14- and 16-membered macrolide antibiotics, including MSn analysis for unprecedented depth of coverage, and complimentary analysis with D2O and H218O labeling to elucidate fragmentation mechanisms. These analyses contrast the behaviors of varying classes of macrolides and highlight how analogues can be identified in relation to similar structures, which will provide utility for future studies of novel macrolides, as well as impurities, metabolites, and degradation products of pharmaceuticals. Graphical Abstract.

Synthesis and antibacterial activities of some novel 17, 18-unsaturated carbonyl compounds derivated from josamycin.

Some novel josamycin derivatives bearing an arylalkyl-type side chain were designed and synthesized. By HWE or Wittig reaction, 16-aldehyde group of josamycin analogs were converted into unsaturated carbonyl compounds. They were evaluated for their in vitro antibacterial activities against a panel of respiratory pathogens. 8b and 8e exhibited comparable activities against a panel of respiratory pathogens, especially to resistant ones in the series of desmycarosyl josamycin analogs. Among of all the target molecules, 21 showed the best antibacterial activities.

Synthesis and antibacterial activity of a series of novel 9-O-acetyl- 4'-substituted 16-membered macrolides derived from josamycin.

A series of novel 9-O-acetyl-4'-substituted 16-membered macrolides derived from josamycin has been designed and synthesized by cleavage of the mycarose of josamycin and subsequent modification of the 4'-hydroxyl group. These derivatives were evaluated for their in vitro antibacterial activities against a panel of Staphylococcus aureus and Staphylococcus epidermidis. 15 (4'-O-(3-Phenylpropanoyl)-9-O-acetyl-desmycarosyl josamycin) and 16 (4'-O-butanoyl-9-O-acetyl-desmycarosyl josamycin) exhibited comparable activities to josamycin against S. aureus (MSSA) and S. epidermidis (MSSE).

Application of liquid chromatography-ion trap mass spectrometry to the characterization of the 16-membered ring macrolide josamycin propionate.

Coupled liquid chromatography and ion trap mass spectrometry (LC/MS) was used for the characterization of the semi-synthetic 16-membered ring macrolide josamycin propionate. On-line identification of impurities in this antibiotic complex was performed with an ion trap mass spectrometer without recourse to time-consuming isolation and purification procedures. Ion trap mass spectrometry is ideally suited to identification of impurities because it provides MSn capability, enabling multiple stages of mass spectrometry to obtain the maximum amount of structural information for a given molecule. The ion trap was used with an electrospray ionization source operated in the positive ion mode or with an atmospheric pressure chemical ionization source operated in the negative ion mode. The identity of the unknown compounds was deduced using the MS/MS and MSn collision-induced dissociation spectra of reference substances or structural analogs as interpretative templates, combined with knowledge about the nature of functional group fragmentation behavior. Given the importance attached to the identification of impurities of unknown identity in pharmaceutical substances, this study is useful for companies producing josamycin propionate. The knowledge of the fragmentation behavior is also of importance in further research on other 16-membered macrolides.

A rapid and sensitive high-pressure liquid chromatographic method for monitoring josamycin levels in plasma.

In this study a new high-pressure liquid chromatographic method for monitoring plasma levels of josamycin is described. Josamycin propionate was used as the internal standard. After being extracted from plasma by chloroform at an alkaline pH, the compounds were easily separated on a reversed-phase column C8. The mobile phase was methanol: citrate-phosphate buffer 0.01 M pH 2.8 (85:15 v/v); and the wavelength 232 nm. The retention time was 2.2 min for josamycin and 2.7 min for josamycin propionate; the chromatogram lasted about 3.5 min. Using this method, concentrations of josamycin up to 0.3 microgram/ml were determined.

Clinical multicentre trial with josamycin propionate in paediatric patients.

Josamycin propionate, a tasteless josamycin derivative suitable for the preparation of paediatric oral suspension, was employed in a large, multicentre clinical study aimed at evaluating the effectiveness and safety of the drug. Two hundred paediatric practitioners participated in the study, and 1908 children (mean age 5.27 years) were treated. Respiratory and pararespiratory infections were the most common diagnosis. The mean daily dose of josamycin was 53.5 mg/kg and the drug was administered for an average of 7.31 days. Josamycin proved to be a highly effective antimicrobial agent for the treatment of infections occurring in paediatric practice, with a success rate of 97.1%. The drug also showed a high degree of acceptance by the young patients and was very well tolerated: only 98 children (5.14%) developed side-effects during the treatment. However, the side-effects observed were reliably attributable to josamycin in only 10 out of 300 subjects who were not receiving other drugs; among these the frequency rate was 3.33%.