Macrolides with 14- and 15-membered ring are characterized by high and extensive tissue distribution, as well as good cellular accumulation and retention. Since macrolide structures do not fit the Lipinski rule of five, macrolide pharmacokinetic properties cannot be successfully predicted by common models based on data for small molecules. Here we describe the development of the first models for macrolide cellular pharmacokinetics. By comparison of cellular accumulation and retention in six human primary cell cultures of leukocytic and lung origin, as well as in lung carcinoma cell line NCI-H292, this cell line was found to be an adequate representative cell type for modeling macrolide cellular pharmacokinetics. Accumulation and retention in the NCI-H292 cells, as well as various physicochemical properties, were determined for a set of 48 rationally designed basic macrolide compounds. Classification models for predicting macrolide cellular accumulation and retention were developed using relatively easily determined and conceptually simple descriptors: experimentally determined physicochemical parameters ChromlogD and CHI IAM, as well as a calculated number of positively charged atoms (POS). The models were further tested and improved by addition of 37 structurally diverse macrolide molecules.
The three-dimensional structures of oleandomycin (1) and its derivatives oleandomycin-9-oxime (2) and 10,11-anhydrooleandomycin (3) were determined in different solvents by the combined use of NMR and molecular modeling methods. The experimental NMR data were compared with the results of molecular modeling and known crystal structures of the related molecules. It was shown that the dominant conformation of the lactone ring is the folded-out conformation with some amounts of the folded-in one depending on the solvent and temperature, while desosamine and cladinose sugars adopt the usual chair conformations. Modeling calculations provided evidence for conformational changes in the upper lactone region as well. Saturation transfer difference (STD) NMR experiments have provided information on the binding epitopes of 1-3 in complexes with E. coli ribosomes. The obtained molecular surfaces in close contact with ribosomes were compared with recently available 3D structures of the related macrolide-ribosome complexes, and the observed differences were discussed. The knowledge gained from this study can serve as a platform for the design of novel macrolides with an improved biological profile.
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