An Unexpected Lewis Acid-Catalyzed Cascade during the Synthesis of the DEF-Benzoxocin Ring System of Nogalamycin and Menogaril: Mechanistic Elucidation by Intermediate Trapping Experiments and Density Functional Theory Studies

An unexpected Lewis acid-catalyzed carbohydrate rearrangement of a 1,5-bis-glycopyranoside to the product of a formal intramolecular C-aryl glycosylation reaction is reported. Mechanistic studies based mainly on intermediate trapping experiments and density functional theory (DFT) calculations reveal a cascade process involving three transient (a)cyclic oxocarbenium cations, the breaking of three single C(sp3)-O bonds, and the formation of three single bonds (i.e., exo-, endo-, and C-glycosidic bonds), leading to the 2,6-epoxybenzoxocine skeleton of bioactive natural glycoconjugates related to serjanione A and mimocaesalpin E. DFT calculations established that the generation of the pyran moiety embedded in the bridged benzoxocin ring system is likely to proceed through an unusual ring-closure of an ortho-quinone methide intermediate in which the attacking nucleophile is a carbonyl oxygen.

Emerging treatment approaches for triple-negative breast cancer

Approximately, 15% of global breast cancer cases are diagnosed as triple-negative breast cancer (TNBC), identified as the most aggressive subtype due to the simultaneous absence of estrogen receptor, progesterone receptor, and HER2. This characteristic renders TNBC highly aggressive and challenging to treat, as it excludes the use of effective drugs such as hormone therapy and anti-HER2 agents. In this review, we explore standard therapies and recent emerging approaches for TNBC, including PARP inhibitors, immune checkpoint inhibitors, PI3K/AKT pathway inhibitors, and cytotoxin-conjugated antibodies. The mechanism of action of these drugs and their utilization in clinical practice is explained in a pragmatic and prospective manner, contextualized within the current landscape of standard therapies for this pathology. These advancements present a promising frontier for tailored interventions with the potential to significantly improve outcomes for TNBC patients. Interestingly, while TNBC poses a complex challenge, it also serves as a paradigm and an opportunity for translational research and innovative therapies in the field of oncology.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2019-2020

This review is the tenth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2020. Also included are papers that describe methods appropriate to analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. The review is basically divided into three sections: (1) general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, quantification and the use of arrays. (2) Applications to various structural types such as oligo- and polysaccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals, and (3) other areas such as medicine, industrial processes and glycan synthesis where MALDI is extensively used. Much of the material relating to applications is presented in tabular form. The reported work shows increasing use of incorporation of new techniques such as ion mobility and the enormous impact that MALDI imaging is having. MALDI, although invented nearly 40 years ago is still an ideal technique for carbohydrate analysis and advancements in the technique and range of applications show little sign of diminishing.

Solvent-Free Approaches in Carbohydrate Synthetic Chemistry: Role of Catalysis in Reactivity and Selectivity

Owing to their abundance in biomass and availability at a low cost, carbohydrates are very useful precursors for products of interest in a broad range of scientific applications. For example, they can be either converted into basic chemicals or used as chiral precursors for the synthesis of potentially bioactive molecules, even including nonsaccharide targets; in addition, there is also a broad interest toward the potential of synthetic sugar-containing structures in the field of functional materials. Synthetic elaboration of carbohydrates, in both the selective modification of functional groups and the assembly of oligomeric structures, is not trivial and often entails experimentally demanding approaches practiced by specialized groups. Over the last years, a large number of solvent-free synthetic methods have appeared in the literature, often being endowed with several advantages such as greenness, experimental simplicity, and a larger scope than analogous reactions in solution. Most of these methods are catalytically promoted, and the catalyst often plays a key role in the selectivity associated with the process. This review aims to describe the significant recent contributions in the solvent-free synthetic chemistry of carbohydrates, devoting a special critical focus on both the mechanistic role of the catalysts employed and the differences evidenced so far with corresponding methods in solution.

Recent progress in chemical synthesis of bacterial surface glycans

With the continuing advancement of carbohydrate chemical synthesis, bacterial glycomes have become increasingly attractive and accessible synthetic targets. Although bacteria also produce carbohydrate-containing secondary metabolites, our review here will cover recent chemical synthetic efforts on bacterial surface glycans. The obtained compounds are excellent candidates for the development of improved structurally defined glycoconjugate vaccines to combat bacterial infections. They are also important probes for investigating glycan-protein interactions. Glycosylation strategies applied for the formation of some challenging glycosidic bonds of various uncommon sugars in a number of recently synthesized bacterial surface glycans are highlighted.

Synthesis of the pentasaccharide repeating unit of the O-antigen from Enterobacter cloacae C4115 containing the rare α-d-FucNAc

Total synthesis of the pentasaccharide repeating unit associated with the O-antigen of Enterobacter cloacae C4115 is reported. The synthesis of the said oligosaccharide was accomplished through rational protecting group manipulations on commercially available monosaccharides followed by stereoselective glycosylations either by activation of thioglycosides or glycosyl trichloroacetimidates and was found to be productive. Towards the synthesis of the rare sugar unit, α-d-FucNAc in this case, it was established that the methoxymethyl (MOM) group is advantageous over the earlier reported tetrahydro pyran (THP) protection. The effect of MOM-protection was successfully tested for the synthesis of a rare sugar synthon which can serve as a precursor to the rare d-fucosamine residue.