Chemoenzymatic synthesis of a trimeric ganglioside GM3 analogue

Improvement of the immune efficacy of carbohydrate vaccines by chemical modification on the GM3 antigen

N-modified GM3 glycoconjugates improved the efficiency of the vaccination without the combination of metabolic oligosaccharide engineering technology.

Synthesis and immunological properties of N-modified GM3 antigens as therapeutic cancer vaccines

The problem of immunotolerance to GM3, an important tumor-associated trisaccharide antigen, seriously hinders its usage in cancer vaccine development. To solve this problem, the keyhole limpet hemocyanin (KLH) conjugates of a series of GM3 derivatives were synthesized and screened as therapeutic cancer vaccines. First, the beta-linked anomeric azides of differently N-acylated GM3 analogues were prepared by a highly convergent procedure. Next, a pentenoyl group was linked to the reducing end of the carbohydrate antigens following selective reduction of the azido group. The linker was thereafter ozonolyzed to give an aldehyde functionality permitting the conjugation of the antigens to KLH via reductive amination. Finally, the immunological properties of the resultant glycoconjugates were studied in C57BL/6 mice by assessing the titers of specific antibodies induced by the GM3 analogues. While KLH-GM3 elicited low levels of immune response, the KLH conjugates of N-propionyl, N-butanoyl, N-iso-butanoyl, and N-phenylacetyl GM3s induced robust immune reactions with antibodies of multiple isotypes, indicating significantly improved and T-cell dependent immune responses that lead to isotype switching, affinity maturation, and the induction of immunological "memory". It was suggested that GM3PhAc-KLH is a promising vaccine candidate for glycoengineered immunotherapy of cancer with GM3 as the primary target.

The total synthesis of ganglioside GM3

Previous syntheses of ganglioside GM3 (NeuAc alpha3Gal beta4Glc beta1Cer) are reviewed, and both chemoenzymatic and chemical total synthetic approaches were investigated. In a chemoenzymatic approach, (2S,3R,4E)-5'''-acetyl-alpha-neuraminyl-(2''' --> 3'')-beta-galactopyranosyl-(1'' --> 4')-beta-glucopyranosyl-(1' <--> 1)-2-azido-4-octadecene-1,3-diol (azidoGM3) was readily prepared utilizing recombinant beta-Gal-(1'' --> 3'/4')-GlcNAc alpha-(2''' --> 3'')-sialyltransferase enzyme, and was evaluated as a synthetic intermediate to ganglioside GM3. The chemical total synthesis of ganglioside GM3 was performed on one of the largest scales yet reported. The highlights of this synthesis include minimizing the steps necessary to prepare the lactosyl acceptor as a useful anomeric mixture, which was present in excess for the highly regioselective and fairly stereoselective sialylation with a known neuraminyl donor to give the protected GM3 trisaccharide. The synthetic methodology maximized convergence by a subsequent glycosidic coupling of the well-characterized GM3 trisaccharide trichloroacetimidate derivative with protected ceramide. The ganglioside GM3 was nearly homogeneous as the two glycosidic couplings utilized preparative HLPC purifications, and variations in the sphingosine base and fatty acyl group were under 0.1 and 0.2%, respectively.