Full details are presented for use of the Bsmoc amino-protecting group for both solid phase and rapid continuous solution syntheses. Application to the latter methodology represents a significant improvement over the corresponding Fmoc-based method for rapid solution synthesis due to the opportunity to use water or saturated sodium chloride solution rather than an acidic phosphate buffer to remove all byproducts, with consequent cleaner phase separation and higher yields of the growing peptide. Comparison of the Bsmoc and Bspoc functions showed that the former, because of steric hindrance, does not suffer from the competitive or premature deblocking observed with the Bspoc system. Because of its incorporation of a styrene chromophore, resin loading of Bsmoc amino acids could be followed as has previously been shown for the Fmoc analogues. Applications of Bsmoc chemistry to peptide sequences incorporating the base sensitive Asp-Gly unit gave less contamination due to aminosuccinimide formation than comparable syntheses involving standard Fmoc chemistry because a weaker or less concentrated base could be used in the deblocking step. Experimental details are presented for building up peptides in solution via the continuous methodology. Deblockings involved the use of insoluble piperazino silica as well as the polyamine TAEA which simplified aqueous separation of the growing, but nonisolated peptide product, from excess acylating agent and other side products formed in the deblocking process. By the appropriate choice of base, one can act selectively at either site of a molecule which incorporates both β-elimination and Michael acceptor sites as protective units (Bsmoc vs Fm and Fmoc vs Bsm).
Mannheimia haemolytica and Pasteurella multocida are aetiological agents commonly associated with respiratory tract infections in cattle. Recent isolates of these pathogens have been shown to be resistant to macrolides and other ribosome-targeting antibiotics. Direct analysis of the 23S rRNAs by mass spectrometry revealed that nucleotide A2058 is monomethylated, consistent with a Type I erm phenotype conferring macrolide-lincosamide resistance. The erm resistance determinant was identified by full genome sequencing of isolates. The sequence of this resistance determinant, now termed erm(42), has diverged greatly from all previously characterized erm genes, explaining why it has remained undetected in PCR screening surveys. The sequence of erm(42) is, however, completely conserved in six independent M. haemolytica and P. multocida isolates, suggesting relatively recent gene transfer between these species. Furthermore, the composition of neighbouring chromosomal sequences indicates that erm(42) was acquired from other members of the Pasteurellaceae. Expression of recombinant erm(42) in Escherichia coli demonstrated that the enzyme retains its properties as a monomethyltransferase without any dimethyltransferase activity. Erm(42) is a novel addition to the Erm family: it is phylogenetically distant from the other Erm family members and it is unique in being a bona fide monomethyltransferase that is disseminated between bacterial pathogens.
Polyalanine sequences of varying length and tethered to a solid support are studied in atomic detail by high-resolution magic angle spinning (HR MAS) NMR. At high densities, it is shown that aggregation of the sequences is at the origin of synthetic difficulties. Decreasing the peptide density by discharging the resin allows study of longer sequences without being hampered by aggregation, and R helix formation has been observed for the (Ala) 12 sequence. This demonstrates that the combined use of solid phase synthesis and high resolution magic angle spinning NMR spectroscopy is a new tool that can be used advantageously in the study of aggregating structures
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