Impact of stereochemistry on the biological activity of novel oleandomycin derivatives

A Robust and Scalable Process for the Synthesis of Substantially Pure Clarithromycin 9-(E)-Oxime with an Established Control of the (Z)-Isomer Impurity

Controlling the isomeric impurity in a key raw material is always critical to achieve the corresponding pure isomer-free targeted active pharmaceutical ingredient (API) in downstream processing. Clarithromycin 9-(E)-oxime is the key raw material for the synthesis of the 9a-lactam macrolide, which is an interesting scaffold for the synthesis of several bioactive macrolides. Here demonstrated is a scalable process for the preparation of substantially pure clarithromycin 9-(E)-oxime, with less than 1.2% of the (Z)-isomer. The process does not involve a separate time-consuming purification by a crystallization operation to purge the undesired (Z)-oxime isomer. Further, the pure clarithromycin 9-(E)-oxime obtained was subjected to the Beckmann rearrangement, thereby converting it into the pure 9a-lactam scaffold. Additionally, a few other impurities were identified and controlled at each stage. The fine-tuned process was successfully up scaled to a multikilogram scale, enabling the large-scale manufacturing of potential APIs derived from this scaffold.

Unprecedented Epimerization of an Azithromycin Analogue: Synthesis, Structure and Biological Activity of 2'-Dehydroxy-5″-Epi-Azithromycin

Certain macrolide antibiotics, azithromycin included, possess anti-inflammatory properties that are considered fundamental for their efficacy in the treatment of chronic inflammatory diseases, such as diffuse pan-bronchiolitis and cystic fibrosis. In this study, we disclose a novel azithromycin analog obtained via Barton-McCombie oxidation during which an unprecedented epimerization on the cladinose sugar occurs. Its structure was thoroughly investigated using NMR spectroscopy and compared to the natural epimer, revealing how the change in configuration of one single stereocenter (out of 16) profoundly diminished the antimicrobial activity through spatial manipulation of ribosome binding epitopes. At the same time, the anti-inflammatory properties of parent macrolide were retained, as demonstrated by inhibition of LPS- and cigarette-smoke-induced pulmonary inflammation. Not surprisingly, the compound has promising developable properties including good oral bioavailability and a half-life that supports once-daily dosing. This novel anti-inflammatory candidate has significant potential to fill the gap in existing anti-inflammatory agents and broaden treatment possibilities.

The impact and fate of clarithromycin in anaerobic digestion of waste activated sludge for biogas production

Clarithromycin retained in waste activated sludge (WAS) inevitably enters the anaerobic digestion system. So far, the complex impacts and fate of clarithromycin in continuous operated WAS anaerobic digestion system are still unclear. In this study, two semi-continuous long-term reactors were set up to investigate the effect of clarithromycin on biogas production and antibiotic resistance genes (ARGs) during WAS anaerobic digestion, and a batch test was carried out to explore the potential metabolic mechanism. Experimental results showed that clarithromycin at lower concentrations (i.e., 0.1 and 1.0 mg/L) did not affect biogas production, whereas the decrease in biogas production was observed when the concentration of clarithromycin was further increased to 10 mg/L. Correspondingly, the relative abundance of functional bacteria in WAS anaerobic digestion (i.e., Anaerolineaceae and Microtrichales) was reduced with long-term clarithromycin exposure. The investigation of ARGs suggested that the effect of methylation belonging to the target site modification played a critical role for the anaerobic microorganisms in the expression of antibiotic resistance, and ermF, played dominated ARGs, presented the most remarkable proliferation. In comparison, the role of efflux pump was weakened with a significant decrease of two detected efflux genes. During WAS anaerobic digestion, clarithromycin could be partially degraded into metabolites with lower antimicrobial activity including oleandomycin and 5-O-desosaminyl-6-O-methylerythronolide and other metabolites without antimicrobial activity.

Recent advances in the discovery and combinatorial biosynthesis of microbial 14-membered macrolides and macrolactones

Macrolides, especially 14-membered macrolides, are a valuable group of antibiotics that originate from various microorganisms. In addition to their antibacterial activity, newly discovered 14-membered macrolides exhibit other therapeutic potentials, such as anti-proliferative and anti-protistal activities. Combinatorial biosynthetic approaches will allow us to create structurally diversified macrolide analogs, which are especially important during the emerging post-antibiotic era. This review focuses on recent advances in the discovery of new 14-membered macrolides (also including macrolactones) from microorganisms and the current status of combinatorial biosynthetic approaches, including polyketide synthase (PKS) and post-PKS tailoring pathways, and metabolic engineering for improved production together with heterologous production of 14-membered macrolides.

Stereochemical Investigations of Diastereomeric N-[2-(Aryl)-5-methyl-4-oxo-1,3-thiazolidine-3-yl]-pyridine-3-carboxamides by Nuclear Magnetic Resonance Spectroscopy (1D and 2D)

Some new N-[2-(aryl)-5-methyl-4-oxo-1,3-thiazolidine-3-yl]-pyridine-3-carboxamides were synthesized and their structures were investigated by IR, NMR (1H, 13C, and 2D), and mass spectra. The presence of C-2 and C-5 stereogenic centers on the thiazolidinone ring resulted in diastereoisomeric pairs. The configurations of two stereogenic centers were assigned based upon 1H NMR analysis of coupling constants and 2D nuclear overhauser enhancement spectroscopy (NOESY) experiment. Resolution of the diastereoisomers was performed by high performance liquid chromatography (HPLC) using a chiral stationary phase.

The design of novel classes of macrolides for neutrophil-dominated inflammatory diseases

Neutrophil-dominated inflammatory diseases, like chronic obstructive pulmonary disease, cystic fibrosis, bronchiectasis, bronchiolitis obliteras syndrome and non-eosinophilic asthma, present a significant medical problem lacking adequate therapy. Macrolide antibiotics have been reported to be effective in the treatment of the aforementioned diseases, for reasons unrelated to their antibacterial action. This has resulted in research activities aimed at gaining a better understanding of the immunomodulatory actions of macrolides and the synthesis of various novel anti-inflammatory macrolides without antimicrobial activity. Despite the difficult chemistry and lack of an extensive knowledge for their mechanism of action, several interesting molecules from this class, including potential clinical candidates, are on the horizon.

Concise synthesis and biological assessment of (+)-neopeltolide and a 16-member stereoisomer library of 8,9-dehydroneopeltolide: identification of pharmacophoric elements

We describe herein a concise synthesis of (+)-neopeltolide, a marine macrolide natural product that elicits a highly potent antiproliferative activity against several human cancer cell lines. Our synthesis exploited the powerful bond-forming ability and high functional group compatibility of olefin metathesis and esterification reactions to minimize manipulations of oxygen functionalities and to maximize synthetic convergency. Our findings include a chemoselective olefin cross-metathesis reaction directed by H-bonding, and a ring-closing metathesis conducted under non-high dilution conditions. Moreover, we developed a 16-member stereoisomer library of 8,9-dehydroneopeltolide to systematically explore the stereostructure-activity relationships. Assessment of the antiproliferative activity of the stereoisomers against A549 human lung adenocarcinoma, MCF-7 human breast adenocarcinoma, HT-1080 human fibrosarcoma, and P388 murine leukemia cell lines has revealed marked differences in potency between the stereoisomers. This study provides comprehensive insights into the structure-activity relationship of this important antiproliferative agent, leading to the identification of the pharmacophoric structural elements and the development of truncated analogues with nanomolar potency.