Access to Versatile β-Cyclodextrin Scaffolds through Guest-Mediated Monoacylation

ANALYSIS OF CARBOHYDRATES AND GLYCOCONJUGATES BY MATRIX-ASSISTED LASER DESORPTION/IONIZATION MASS SPECTROMETRY: AN UPDATE FOR 2015-2016

This review is the ninth 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 2016. 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. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation and arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals. Much of this material is presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions and applications to chemical synthesis. The reported work shows increasing use of combined new techniques such as ion mobility and the enormous impact that MALDI imaging is having. MALDI, although invented over 30 years ago is still an ideal technique for carbohydrate analysis and advancements in the technique and range of applications show no sign of deminishing. © 2020 Wiley Periodicals, Inc.

Yb(OTf)3-Catalyzed and Di-tert-butyl Dicarbonate-Mediated Decarboxylative Etherification and Esterification Reactions

Protecting group chemistry has invariably captured the fascination of chemists because of its extensive viability in chemical synthesis. The present report describes our pioneer work of applying ytterbium triflate as a catalyst, for the reaction of alcohols with di-tert-butyl dicarbonate (Boc2O) leading to the formation of tert-butyl ethers. There exists no recorded evidence for the use of Yb(OTf)3 as a catalyst for the protection of alcohols to tert-butyl ethers, despite its excellent utility in various reactions. Yb(OTf)3 has been used predominantly in the catalytic deprotection studies such as selective deprotection of tert-butyl esters to carboxylic acids as well as prenyl ethers to alcohols. This study involved the critical evaluation of solvent, time, and temperature that finally led to an efficient protocol for the formation of tert-butyl ethers. Yb(OTf)3 catalyzed the formation of tert-butyl ethers, notably reducing the reaction time, which is exemplified by the achievement of up to 92% conversion of alcohols to tert-butyl ethers within an hour. Additionally, the report demonstrates the utility of this synthetic protocol for the protection of carboxylic acids.

Highly Functionalized β-Cyclodextrins by Solid-Supported Synthesis

Using covalent capture, a high yielding selective mono-functionalization of heptakis-[6-deoxy-6-(2-aminoethylsulfanyl)]-β-CD with a 5-mercaptopentyl functional group has been achieved. Here, we demonstrate the immobilization of the mono-thiol functionalized β-CD on PEGA resin via a disulfide bond, enabling solid-phase elaboration of the remaining six primary amines. To showcase the potential of this method, the amines were elaborated to tripeptides through standard Fmoc-peptide chemistry. A small library of CD-tripeptide conjugates was generated which, when reduced from the solid support, could be tagged at the released thiol with an environmentally sensitive fluorophore. The resulting library of sensors showed potential for the differential sensing of various bile salts. The described methodology provides a rapid and versatile route to synthesize highly functionalized libraries of CD derivatives that may be tailored towards applications in sensing, catalysis, and multivalent displays.