Michiel A. Leeuwenburgh

Bioorthogonal organic chemistry in living cells: novel strategies for labeling biomolecules

The chemical labeling of biomolecules continues to be an important tool for the study of their function and cellular fate. Attention is increasingly focused on labeling of biomolecules in living cells, since cell lysis introduces many artefacts. In addition, with the advances in biocompatible synthetic organic chemistry, a whole new field of opportunity has opened up, affording high diversity in the nature of the label as well as a choice of ligation reactions. In recent years, several different two-step labeling strategies have emerged. These rely on the introduction of a bioorthogonal attachment site into a biomolecule, then ligation of a reporter molecule to this site using bioorthogonal organic chemistry. This Perspective focuses on these techniques, their implications and future directions.

A NOVEL AND FLEXIBLE SYNTHESIS OF PYRANOSE SPIROACETAL DERIVATIVES

Abstract A three-step approach to chiral pyranose [5,4], [5,5], [5,6] and [5,7] unsaturated spiroacetal derivatives from perbenzylated glucopyranolactone 1 is presented. The strategy involves Grignard addition of vinyl or allyl magnesium bromide to 1 to give 2 and 12 , respectively, K-10 mediated glucosidation of different terminal alkenols with 2 and 12 followed by ring-closing metathesis.

Leukocyte Cathepsin S Is a Potent Regulator of Both Cell and Matrix Turnover in Advanced Atherosclerosis

Objective—A dysbalance of proteases and their inhibitors is instrumental in remodeling of atherosclerotic plaques. One of the proteases implicated in matrix degradation is cathepsin-S (CatS). To address its role in advanced lesion composition, we generated chimeric LDLr−/− mice deficient in leukocyte CatS by transplantation with CatS−/−×LDLr−/− or with LDLr−/− bone marrow and administered a high-fat diet. Methods and Results—No difference in aortic root lesion size could be detected between CatS+/+ and CatS−/− chimeras. However, leukocyte CatS deficiency markedly changed plaque morphology and led to a dramatic reduction in necrotic core area by 77% and an abundance of large foam cells. Plaques of CatS−/− chimeras contained 17% more macrophages, 62% less SMCs, and 33% less intimal collagen. The latter two could be explained by a reduced number of elastic lamina fractures. Moreover, macrophage apoptosis was reduced by 60% with CatS deficiency. In vitro, CatS was found to be involved in cholesterol metabolism and in macrophage apoptosis in a collagen and fibronectin matrix. Conclusion—Leukocyte CatS deficiency results in considerably altered plaque morphology, with smaller necrotic cores, reduced apoptosis, and decreased SMC content and collagen deposition and may thus be critical in plaque stability.

An expeditious route to the synthesis of highly functionalized chiral oxepines from monosaccharides

Abstract The transformation of partially protected aldofuranoses into dienes by Wittig olefination of the anomeric center followed by either allylation or oxopalladation of alkoxy-1,2-propadienes is described. Ring-closing metathesis of the linear dienes gives rise to a variety of highly functionalized and chiral ring-expanded oxepines.

A convenient route to cis- and trans-fused bicyclic ethers by ruthenium mediated ring-closing metathesis of diene and enyne carbohydrate derivatives

Abstract A general approach towards the construction of highly functionalised pyranopyran and pyranofuran systems via Grubbs [Ru] catalysed ring-closing metatheses of neighbouring vinyl-O-allyl and vinyl-O-propargyl functions on monosaccharide scaffolds is described.

A novel approach towards the stereoselective synthesis of 2-azido-2-deoxy-β-d-mannosides

Low temperature mannosylation of glycosyl acceptors under the agency of S-(4-methoxyphenyl) benzenethiosulfinate (MPBT) and trifluoromethanesulfonic anhydride (Tf2O) with p-methoxyphenyl 2-azido-3-O-benzyl-4,6-O-benzylidene-2-deoxy-1-thio-α-d-mannopyranoside, readily available from d-mannosamine hydrochloride, affords 2-azido-2-deoxy-d-mannosides with high β-selectivity in good yields.

Rhodium(II) catalyzed asymmetric cyclopropanation of glycals with ethyl diazoacetate

Abstract Carbenoid species generated from ethyl diazoacetate and catalytic Rh 2 (OAc) 4 react smoothly and with a high degree of stereoselectivity with glycals resulting in the predominant formation of doubly branched adducts containing an α- exo -orientated ethyl cyclopanecarboxylate moiety.

Stereoselective Synthesis of α-C-(alkynyl)-glycosides via Ring-opening of α-1,2-Anhydrosugars

Ring-opening of an α-1,2-epoxide function in sugars with lithium alkynyl derivatives in the presence of zinc chloride proceeds with retention of configuration to afford α-C-(alkynyl)-glycosides in reasonable yields.

A Short and Flexible Route to Aza‐β‐(1→6)‐C‐disaccharides: Selective α‐Glycosidase Inhibitors

The syntheses of azaMan-beta-(1-->6)-C-Glc (4), azaGlc-beta-(1-->6)-C-Glc (5), and azaGal-beta-(1-->6)-C-Glc (6) based upon double reductive amination of acetylenic carbohydrate-derived diketones is described. The required diketones are obtained by addition of the acetylenic sugar anion derived from dibromoolefin 7 to benzyl-protected mannopyranolactone, glucopyranolactone, or galactopyranolactone, followed by reduction of the ketose and oxidation of the resulting diol. Ensuing double reductive amination and hydrogenolysis affords the target compounds in reasonable to good yields. Enzyme inhibition tests show that neither of the three compounds 4, 5, and 6 inhibit beta-glycosidases, while moderate to good inhibitory activities were found on alpha-glycosidases, the most active being 6 (alpha-galactosidase: K-i = 0.092 mu M).

Synthesis of Tetrameric Arabinogalactans Based on 1,2‐Anhydrosugars

The spacer-containing tetrameric arabinogalactans 1−3, suitable for CCRC-M7 epitope characterization, are readily accessible by ZnCl2-assisted stepwise elongation of 11-methoxycarbonylundecanol 9 with the 1,2-anhydrogalactose building unit 6. NIS/cat. TfOH-mediated glycosylation of the newly formed 2-OH, 2′-OH, or 2′′-OH function in the β-(16)-galactoside backbone with the 1-thioarabinofuranoside donor 8, followed by deprotection, provided the target tetramers in high overall yield.