Glycosyl Imidates, 75. Synthesis of the Hexasaccharide Moiety of Globo H (Human Breast Cancer) Antigen

Continuous synthesis of bromoalkyl glycosides by Fischer glycosylation in a microreactor

In this study, bromoalkyl glycosides were successfully synthesized in microreactor scale by Fischer glycosylation. Yields between 24 and 40% after purification were achieved using various acidic catalysts and conditions. In some experiments, yields 180% higher than with previously known methods could be achieved. This study showed also that reversed-phase flash chromatography is more successful than normal-phase flash chromatography for the purification of bromoalkyl glycosides. Furthermore, longer bromoalcohols were shown to be more compatible than shorter bromoalcohols under these reaction conditions.

Synthesis and immunological evaluation of N-acyl modified Globo H derivatives as anticancer vaccine candidates

Globo H is a tumor-associated carbohydrate antigen (TACA), which serves as a valuable target for antitumor vaccine or cancer immunotherapies. However, most TACAs are T-cell-independent, and they cannot induce powerful immune response due to their poor immunogenicity. To address this problem, herein, several Globo H analogues with modification on the N-acyl group were prepared through a preactivation-based glycosylation strategy from the non-reducing end to the reducing end. These modified Globo H derivatives were then conjugated with carrier protein CRM197 to form glycoconjugates as anticancer vaccine candidates, which were used in combination with adjuvant glycolipid C34 for immunological studies. The immunological effects of these synthetic vaccine candidates were evaluated on Balb/c mice. The results showed that the fluorine-modified N-acyl Globo H conjugates can induce higher titers of IgG antibodies that can recognize the naturally occurring Globo H antigen on the surface of cancer cells and can eliminate cancer cells in the presence of a complement, indicating the potential of these synthetic glycoconjugates as anticancer vaccine candidates.

Fast and Low-Cost Purification Strategy for Oligosaccharide Synthesis Based on a Hop-On/Off Carrier

A feasible and convenient strategy for oligosaccharide synthesis, which realizes reaction in solution while product purification occurs only by solid-liquid filtration, has been developed. By using a hop-on/off carrier (polytetrafluoroethylene particle), rapid synthesis of tumor-associated antigen Globo-H hexasaccharide has been successfully achieved within 5 steps in 48% overall yield without any intermediate purification by column chromatography. Also, global deprotection, including the cleavage of the tag, proceeded simultaneously only by one-step hydrogenolysis.

Chemical glycosylation in the synthesis of glycoconjugate antitumour vaccines

Therapeutic vaccines derived from carbohydrate antigen-adjuvant combinations are a promising approach for cancer immunotherapy. One of the critical limitations in this area is access to sufficient quantities of tumour-associated carbohydrate antigens and glycoconjugate adjuvants. At present, availability of the complex oligosaccharide constructs that are needed for the systematic design and evaluation of novel vaccine formulations relies on de novo chemical synthesis. The use of both state-of-the-art and emerging glycosylation technologies has led to significant advances in this field, allowing the clinical exploration of carbohydrate-based antigens in the treatment of cancer.

Carbohydrate microarray for profiling the antibodies interacting with Globo H tumor antigen

Understanding the specificity of cell-surface carbohydrates interaction with antibodies and receptors is important for the development of new therapeutics and high-sensitivity diagnostics. This approach is, however, limited to the availability of natural and truncated sequences of the oligosaccharides and the sensitivity of the assay system. Reported here is the synthesis of the cancer antigen Globo H hexasaccharide, an epitope found on the cell surface of breast, prostate, and ovarian cancers, and its truncated sequences by using the programmable one-pot synthesis strategy. The saccharides were then arrayed covalently on glass slides with different density and used for the fluorencense-based binding analysis of two monoclonal antibodies against Globo H and the serum from breast cancer patients, to define the specificity of these antibodies. It was shown that the terminal tetrasaccharide binds the monoclonal antibodies equally well as does the hexasaccharide and the fucose residue is required for effective binding. The serum binds both the defucosylated pentasaccharide and the fucosylated hexasaccharide without a significant difference, perhaps because of the polyclonal nature of the serum or the presence of diverse immune responses to different sugar epitopes at various stages. This method requires very small amounts of materials and is more effective and sensitive than the traditional ELISA method, and thus provides another platform to monitor the immune response to carbohydrate epitopes at different stages during differentiation, metastasis, or treatment.

Automated synthesis of oligosaccharides as a basis for drug discovery

Carbohydrates present both potential and problems - their biological relevance has been recognized, but problems in procuring sugars rendered them a difficult class of compounds to handle in drug discovery efforts. The development of the first automated solid-phase oligosaccharide synthesizer and other methods to assemble defined oligosaccharides rapidly has fundamentally altered this situation. This review describes how quick access to oligosaccharides has not only contributed to biological, biochemical and biophysical investigations, but also to drug discovery. Particular focus will be placed on the development of carbohydrate-based vaccines, defined heparin oligosaccharides and aminoglycosides that have recently begun to affect drug discovery.