Synthesis of the N-terminal glycopentapeptides of human glycophorin am and an carrying trimeric sialosyl Tn epitope

Chemoenzymatic Synthesis of SARS-CoV-2 Homogeneous O-Linked Glycopeptides for Exploring Their Inhibition Functions

Harnessing highly conserved peptides derived from the receptor binding domain (RBD) of spike (S) protein to construct peptide-based inhibitors is one of the most effective strategies to fight against the ever-mutating coronavirus SARS-CoV-2. But how the O-glycosylation affects their inhibition abilities has not been intensively explored. Herein, an intrinsic O-glycosylated peptide P_320-334 derived from RBD was screened and homogeneous O-linked glycopeptides containing Tn (GalNAcα1-O-Ser/Thr), T (Galβ1-3GalNAcα1-O-Ser/Thr), sialyl-Tn (sTn, Siaα2-6GalNAcα1-O-Ser/Thr), and sialyl-T (sT, Siaα2-3Galβ1-3GalNAcα1-O-Ser/Thr) structures were first synthesized via chemoenzymatic strategies. Compared with the unglycosylated peptide, the binding of sT-P_320-334 to hACE2 was enhanced to 133% and the inhibition capacity against RBD-hACE2 binding of sTn- and sT-P_320-334 was significantly increased up to 150-410%. Thus, our results suggest the sialic acid residue on the terminal of short O-glycan structures might strengthen the inhibition capacities of these peptide-based inhibitors, which might provide novel optimization directions for the inhibitor design.

Solution-Phase Synthesis with Solid-State Workup of an O-Glycopeptide with a Cluster of Cancer-Related T Antigens

An N-terminal glycopeptide of asialoglycophorin AM with three O-linked T antigens was prepared by "solution-phase synthesis with solid-state workup" using unprotected glycosyl amino acids as building blocks. For the glycopeptide assembly, all reactions were conducted in homogeneous NMP solutions, while the product of each reaction was readily isolated as solid precipitates upon addition of diethyl ether. In the preparation of building blocks, a robust approach was established to selectively alpha-glycosylate Ser and Thr derivatives. [reaction: see text]

Synthesis of a Mimic for the Heterogeneous Surface of Core 2 Sialoglycan-Linked Glycoprotein

[structure: see text] An O-glycosylated peptide carrying two core 2 sialopentasaccharides of different glycoform was synthesized as a model of the heterogeneous surface of mucin glycoprotein. Solid-phase synthesis and the subsequent enzymatic sialylation gave two segments, which were coupled by selective thioester activation to produce the title compound.

A substrate combinatorial array for caspases

An efficient strategy for the synthesis of a tetrapeptidyl substrate combinatorial array directed toward the caspases is described. Testing of this array with caspases 1 and 4 gave substrate hydrolytic profiles characteristic of each caspase, and permitted the identification of efficiently processed substrates. A comparison of this approach to that using a positional scanning library is presented.

Recombinant blood group antigens are useful for studying the fine specificity of antibodies against glycophorin A encoded antigens

Recombinant wild-type and variant forms of glycophorin A (GPA) were expressed in wild-type and glycosylation-defective Chinese hamster ovary cells. The binding to recombinant GPA of antibodies submitted to the Third International Workshop was assessed by immunoprecipitation and indirect immunofluorescence. This is a powerful approach for determining the fine specificity of antibodies to blood group antigens. The advantages and limitations of this approach are discussed.

Solid-phase synthesis of an O-linked glycopeptide based on a benzyl-protected glycan approach

The solid-phase synthesis of asialo-[Ala18]-B-chain (2) of human alpha 2HS glycoprotein is described. Disaccharide-linked serine unit 12, carrying a benzyl protecting group, was synthesized via stereoselective glycosylation of 8 with 6. Peptide synthesis was carried out by the Fmoc method utilizing an automated peptide synthesizer. A modified procedure using a mechanical shaker at the coupling step with 12 made easy the recovery of unreacted 12. The benzylated glycopeptide thus synthesized was cleaved from the resin and hydrogenated to give 2.

Stereoselective synthesis of a blood group A type glycopeptide present in human blood mucin

N,N-Dimethyl-O-(2-acetamido-2-deoxy-alpha-D-galactopyranosyl)-(1-->3)-O- [(alpha-L-fucopyranosyl)-(1-->2)]-O-(beta-D-galactopyranosyl)-(1-->3)-O- (2-acetamido-2-deoxy-alpha-D-galactopyranosyl)-(1-->3)-L-serine, a core I glycotetraosyl peptide structure and a predominant substructure in complex glycan-glycoproteins present in human blood group A ovarian mucin, was synthesized for the first time. The title compound was synthetically accomplished via the following key manoeuvres: regio- and stereo-controlled construction of the alpha-GalNAc-(1-->3)-Gal synthon, stereoselective glycosylation generating a alpha-GalN3-(1-->3)-Ser glycopeptide synthon and alpha-selective fucosylation towards an acceptor which was derived from glycosylation of the latter two synthons. An alternative route to that of the latter, to synthesize a fully protected equivalent of the title compound, involving the coupling of a alpha-GalNAc-(1-->3)-beta-Gal-(1-->3)-GalN3X synthon to an aglycon serine derivative, is described herein.

Solid-phase synthesis of a glycosylated hexapeptide of human sialophorin, using the trichloroacetimidate method

A hexapeptide containing a beta-D-Gal p-(1-->3)-alpha-D-Gal pNAc-(1-->O)-L-threonine unit was synthesized using glycosylated pentafluorophenyl esters in an Fmoc-based strategy. In all of the glycosylation reactions, trichloroacetimidates were successfully employed. The disaccharide moiety was prepared from tetra-O-acetyl-alpha-D-galactopyranosyl trichloroacetimidate and tert-butyldimethylsilyl 2-azido-6-O-benzoyl-2-deoxy-beta-E-galactopyranoside with boron trifluoride etherate as a catalyst. The glycosylated active esters were obtained in the reaction of alpha and beta 2,3,4,6-tetra-O-acetyl-beta-D-galactopyranosyl-(1-->3)-4-O-acetyl-2-azid o-6- O-benzoyl-2-deoxy-D-galactopyranosyl trichloroacetimidates with Fmoc-protected pentafluorophenyl esters of L-serine and L-threonine in the presence of trimethylsilyl trifluoromethanesulfonate as Lewis acid. The glycosylated pentafluorophenyl ester of L-threonine was transformed into glycopeptides via a solid-phase synthesis. Azide reduction and N-acetylation were performed on the solid phase with a thioacetic acid-pyridine mixture. The glycopeptide was then cleaved from the resin with strong acid, also removing the acid-labile protecting groups of the peptide chain. Finally, the acyl groups used for sugar protection were cleaved with sodium methoxide, affording the completely deprotected N-acetyl-L-leucyl-L-glutamyl-O-[beta-D-galactopyranosyl-(1-->3)-2- acetamido-2-deoxy-alpha-D-galactopyranosyl]-L-threonyl-L-seryl-L-threony l- glycinamide (1) in high purity.