Glycopeptide drugs: A pharmacological dimension between "Small Molecules" and "Biologics"

Peptides are an important class of molecules with diverse biological activities. Many endogenous peptides, especially neuropeptides and peptide hormones, play critical roles in development and regulating homeostasis. Furthermore, as drug candidates their high receptor selectivity and potent binding leads to reduced off-target interactions and potential negative side effects. However, the therapeutic potential of peptides is severely hampered by their poor stability in vivo and low permeability across biological membranes. Several strategies have been successfully employed over the decades to address these concerns, and one of the most promising strategies is glycosylation. It has been demonstrated in numerous cases that glycosylation is an effective synthetic approach to improve the pharmacokinetic profiles and membrane permeability of peptides. The effects of glycosylation on peptide stability and peptide-membrane interactions in the context of blood-brain barrier penetration will be explored. Numerous examples of glycosylated analogues of endogenous peptides targeting class A and B G-protein coupled receptors (GPCRs) with an emphasis on O-linked glycopeptides will be reviewed. Notable examples of N-, S-, and C-linked glycopeptides will also be discussed. A small section is devoted to synthetic methods for the preparation of glycopeptides and requisite amino acid glycoside building blocks.

Glycomics using mass spectrometry

Mass spectrometry plays an increasingly important role in structural glycomics. This review provides an overview on currently used mass spectrometric approaches such as the characterization of glycans, the analysis of glycopeptides obtained by proteolytic cleavage of proteins and the analysis of glycosphingolipids. The given examples are demonstrating the application of mass spectrometry to study glycosylation changes associated with congenital disorders of glycosylation, lysosomal storage diseases, autoimmune diseases and cancer.

Infrared Multiphoton Dissociation and Electron Capture Dissociation of High-Mannose Type Glycopeptides

The combination of electron capture dissociation (ECD) and infrared multiphoton dissociation (IRMPD) for the structural characterization of high-mannose type glycopeptides is explored in depth for the first time. Contrary to previous applications to other glycan types, our analyses reveal that IRMPD does not necessarily selectively induce glycan cleavage in high-mannose type glycopeptides; rather peptide backbone cleavage can effectively compete with glycosidic cleavage. Poor glycan cleavage with IRMPD is due to a higher gas-phase stability of mannose-linking glycosidic bonds. This reasoning also explains mannose cleavage patterns observed for a xylose type glycopeptide with IRMPD. In addition, extensive peptide backbone cleavage is observed for a >6 kDa glycopeptide with ECD, to our knowledge the largest glycopeptide examined with this technique to date.

A thin chip microsprayer system coupled to Fourier transform ion cyclotron resonance mass spectrometry for glycopeptide screening

A thin polymer microchip was coupled with a Fourier transform ion cyclotron resonance (FTICR) 9.4 T mass spectrometer and the method was optimized in negative ion mode for glycopeptide screening. The interface between the polymer microchip and FTICR mass spectrometer consists of an in-laboratory conceived and designed mounting system that exhibits robust and controllable alignment of the chip toward the inlet of the mass spectrometer. The particular attribute of the polymer chip coupled to the FTICR mass spectrometer, to achieve an increase in ionization efficiency and sensitivity under the premise of high mass accuracy of detection, is highlighted by the large number of major and minor glycopeptide structures detected and identified in highly heterogeneous mixtures obtained from urine matrices. Glycoforms expressing various saccharide chain lengths ranging from tri- to dodecasaccharide, bearing up to three sialic acid moieties, could be detected and assigned based on the accuracy of the mass measurement (average mass deviation below 6 ppm) of their molecular ions. -Thin chipESI-FTICRMS is a potent novel system for glycomic screening of complex mixtures, as demonstrated for identification of singly sialylated O-glycosylated amino acids and peptides from urine matrices, and could be considered for general applicability in the glycoanalytical field.

[Eremomycin--a new antibiotic of the polycyclic glycopeptide group]

Eremomycin is a novel antibacterial antibiotic. It was isolated at the Institute of New Antibiotics, the USSR Academy of Medical Sciences from the culture fluid of actinomycete INA-238. By its physico-chemical and biological properties the antibiotic was classified as belonging to the group of polycyclic glycopeptides. Chemical structure of eremomycin was asserted and it was shown to be a new representative of the group close by its structure to vancomycin and differing from it by the carbohydrate composition and structure of tri-phenoxytriaminotricarboxylic acid. By its anti-bacterial spectrum eremomycin was found to be close to ristomycin and vancomycin. Still, its activity was 2-10 times higher. The antibiotic was several times less toxic than vancomycin. Unlike vancomycin and ristomycin, the novel antibiotic induced no tissue necrosis after its intramuscular administration. The chemotherapeutic indices of eremomycin in treatment of staphylococcal and streptococcal sepsis in albino mice exceeded 10 times those of vancomycin. At present eremomycin is under clinical trials.