ofeng Gu

Silver triflate. A mild alternative catalyst for glycosylation conditions using trichloroacetimidates as glycosyl donors

Although trimethylsilyl triflate (TMSOTf) has been widely used to promote glycosyl trichloroacetimidates in oligosaccharide synthesis, silver triflate (AgOTf) was proved to be a mild and in some cases more efficient catalyst in TMSOTf‐sensitive glycosylations. Migration and degradation in some specific coupling reactions can be reduced significantly under this alternative glycosylation condition.

Synthesis of a hexasaccharide that relates to the arabinogalactan epitope

A hexasaccharide derivative of the arabinogalactan epitope, methyl beta-D-galactopyranosyl-(1-->6)-[alpha-L-arabinofuranosyl-(1-->3)]-beta-D-galactopyranosyl-(1-->6)-beta-D-galactopyranosyl-(1-->6)-[alpha-L-arabinofuranosyl-(1-->3)]-alpha-D-galactopyranoside, was synthesized efficiently using a 3+3 strategy. The key step is the preparation of the trisaccharide donor, isopropyl 2,3,4,6-tetra-O-benzoyl-beta-D-galactopyranosyl-(1-->6)-[2,3,5-tri-O-benzoyl-alpha-L-arabinofuranosyl-(1-->3)]-2,4-di-O-benzoyl-1-thio-beta-D-galactopyranoside, from isopropyl 1-thio-beta-D-galactopyranoside using a one-pot synthesis of a 3,6-differentially protected building block.

Synthetic and Immunological Studies of Mycobacterial Lipoarabinomannan Oligosaccharides and Their Protein Conjugates.

Lipoarabinomannan (LAM) is one of the major constituents of the Mycobacterium tuberculosis cell wall and an attractive molecular scaffold for antituberculosis drug and vaccine development. In this paper, a convergent strategy was developed for the synthesis of LAM oligosaccharides with an α-1,2-linked dimannopyranose cap at the nonreducing end. The strategy was highlighted by efficient coupling of separately prepared nonreducing end and reducing end oligosaccharides. Glycosylations were mainly achieved with thioglycoside donors, which gave excellent yields and stereoselectivity even for reactions between complex oligosaccharides. The strategy was utilized to successfully synthesize tetra-, hepta-, and undecasaccharides of LAM from d-arabinose in 10, 15, and 14 longest linear steps and 7.84, 7.50, and 2.59% overall yields, respectively. The resultant oligosaccharides with a free amino group at their reducing end were effectively conjugated with carrier proteins, including bovine serum albumin and keyhole limpet hemocyanin (KLH), via a bifunctional linker. Preliminary immunological studies on the KLH conjugates revealed that they could elicit robust antibody responses in mice and that the antigen structure had some influence on their immunological property, thus verifying the potential of the oligosaccharides for vaccine development and other immunological studies.

Synthesis of 2-chloro-4-nitrophenyl α-l-fucopyranoside: a substrate for α-l-fucosidase (AFU)

Abstract An effective method to prepare the substrate of α- l -fucosidase (AFU) is described. Ethyl 1-thiofucoside with a free 2-OH group was used as the glycosyl donor, and there was found no self-condensed side product. The use of the HF·pyridine reagent to remove the silyl protecting group in the last step afforded a target molecule of high purity.

Concise synthesis of a buffalo milk pentasaccharide derivative

An efficient synthesis of buffalo milk pentasaccharide derivative via a 3+2 strategy is described. The use of a trisaccharide isopropyl thioglycoside as a latent glycosyl donor and the application of two well-defined regioselective glycosylations significantly simplified the target preparation.

Recent Development in the Synthesis of Natural Saponins and Their Derivatives

Naturally occurring saponins are attractive candidates or lead compounds for new drug design and development and thus have become important synthetic targets. This short account reviews the recent progress in the chemical synthesis and structure-activity relationship (SAR) studies of naturally occurring saponins and their derivatives.

Efficient one-pot synthesis of tigogenin saponins and their antitumor activities

An efficient synthesis of naturally occurring tigogenin triglycoside 1a and its three derivatives 1b-d bearing different carbohydrate moieties, as well as their antitumor activities, is described. Partially protected thiogalactosides bearing unprotected 2,4-OH or 4-OH groups were used to facilitate regioselective reactions for one-pot sequential multi-step glycosylation, which has significantly simplified the target molecule synthesis. The synthetic saponins 1a-d exhibited much higher anti-tumor activities than the positive control cisplatin against the human epithelial cervical cancer cell (HeLa) as evaluated by CCK-8 assay.

Facile Synthesis and Antitumor Activities of Timosaponin AIII and Its Analogs

An efficient synthesis of timosaponin AIII (TAIII) and five structurally modified analogs via a one-pot sequential glycosylation strategy is described. A partially protected D-galactopyranosyl thioglycoside was employed for regioselective glycosylation to facilitate the target synthesis. The antitumor activities of the synthetic saponins against human epithelial cervical cancer cell (HeLa) were preliminarily evaluated by means of CCK-8 assay. An L-rhamnosyl analog was discovered to display stronger inhibitory activity (IC50 3.3 μM) than TAIII (IC50 10.7 μM) to HeLa cell. Supplemental materials are available for this article. Go to the publishers online edition of Journal of Carbohydrate Chemistry to view the free supplemental file.

Efficient and selective removal of chloroacetyl group promoted with tetra-n-butylammonium fluoride (TBAF)

A practical method for the efficient and selective cleavage of chloroacetyl protecting group using tetra-n-butylammonium fluoride (TBAF) in THF solution at rt was disclosed.

Mechanical enhancement and in vitro biocompatibility of nanofibrous collagen-chitosan scaffolds for tissue engineering

Abstract The collagen–chitosan complex with a three-dimensional nanofiber structure was fabricated to mimic native ECM for tissue repair and biomedical applications. Though the three-dimensional hierarchical fibrous structures of collagen–chitosan composites could provide more adequate stimulus to facilitate cell adhesion, migrate and proliferation, and thus have the potential as tissue engineering scaffolding, there are still limitations in their applications due to the insufficient mechanical properties of natural materials. Because poly (vinyl alcohol) (PVA) and thermoplastic polyurethane (TPU) as biocompatible synthetic polymers can offer excellent mechanical properties, they were introduced into the collagen–chitosan composites to fabricate the mixed collagen/chitosan/PVA fibers and a sandwich structure (collagen/chitosan-TPU-collagen/chitosan) of nanofiber in order to enhance the mechanical properties of the nanofibrous collagen–chitosan scaffold. The results showed that the tensile behavior of materials was enhanced to different degrees with the difference of collagen content in the fibers. Besides the Young’s modulus had no obvious changes, both the break strength and the break elongation of materials were heightened after reinforced by PVA. For the collagen–chitosan nanofiber reinforced by TPU, both the break strength and the Young’s modulus of materials were heightened in different degrees with the variety of collagen content in the fibers despite the decrease of the break elongation of materials to some extent. In vitro cell test demonstrated that the materials could provide adequate environment for cell adhesion and proliferation. All these indicated that the reinforced collagen–chitosan nanofiber could be as potential scaffold for tissue engineering according to the different mechanical requirements in clinic.