A versatile synthesis of αGalCer and its analogues exploiting a cyclic carbonate as phytosphingosine 3,4-diol protecting group

Rapid and Stereoselective Access to 6″-Amino-6″-deoxy-α-GalCer Scaffolds

This work describes a highly efficient route to an orthogonally protected α-galactosylphytosphingosine (α-GalPhyt) from which 6″-N-modified α-galactosylceramide (α-GalCer) analogues can be synthesized rapidly and on-scale. Key to this route is the use of a d-galactal-derived 1,2-anhydro donor that undergoes an α-selective glycosylation with a sphingoid acceptor. The resulting α-GalPhyt intermediate can be orthogonally deprotected, enabling selective manipulation at either the C-6″ position of the galactose ring or at C-2 of the sphingoid lipid. The utility of this approach was demonstrated by the synthesis of the potent natural killer (NK) T cell agonist, NU-α-GalCer, and a novel 6″-amino-6″-deoxy analogue of another notable agonist, 7DW8-5, both from the same key intermediate.

Iodine-triphenylphosphine triggers an easy one-pot alpha stereoselective dehydrative glycosylation on hemiacetalic benzylated glycosyl donors

The discovery of new glycosylation reactions is still a major challenge in carbohydrate chemistry. Traditional glycosylation reactions require the preparation of sugar donors with anomeric active or latent leaving groups. Dehydrative glycosylation is a fascinating alternative that enables the direct formation of the glycosidic bond from the hemiacetal, eliminating the need for (sometimes unstable) leaving groups, and allowing to reduce reaction, work-up, and purification times. Although some interesting methods of dehydrative glycosylation have been reported, in order to compete with conventional chemical glycosylation, a greater number of efficient and stereoselective methods need to be developed. Herein, a dehydrative procedure that uses a combination of iodine, triphenylphosphine, and a base (DMAP or imidazole) is described. This methodology allows for the preparation of sugar derivatives from commercially available 1-hydroxy glycosyl donors. The reaction takes place under mild conditions through the in situ-formation of an anomeric iodide intermediate, which, upon reaction with an alcohol, gives the corresponding glycosides up to quantitative yields and with high α-stereoselectivity.

A Lysosome-Targeted Tetrazine for Organelle-Specific Click-to-Release Chemistry in Antigen Presenting Cells

Bioorthogonal deprotections are readily used to control biological function in a cell-specific manner. To further improve the spatial resolution of these reactions, we here present a lysosome-targeted tetrazine for an organelle-specific deprotection reaction. We show that trans-cyclooctene deprotection with this reagent can be used to control the biological activity of ligands for invariant natural killer T cells in the lysosome to shed light on the processing pathway in antigen presenting cells. We then use the lysosome-targeted tetrazine to show that long peptide antigens used for CD8⁺ T cell activation do not pass through this organelle, suggesting a role for the earlier endosomal compartments for their processing.

Sex-Specific Differences in Cytokine Induction by the Glycolipid Adjuvant 7DW8-5 in Mice

7DW8-5 is a potent glycolipid adjuvant that improves malaria vaccine efficacy in mice by inducing IFN-γ and increasing protective CD8⁺ T cell responses. The addition of 7DW8-5 was previously shown to improve the efficacy of a CD8⁺ T cell-mediated heterologous 'prime-and-trap' malaria vaccine against Plasmodium yoelii sporozoite challenge in inbred female mice. Here, we report significant differential sex-specific responses to 7DW8-5 in inbred and outbred mice. Male mice express significantly less IFN-γ and IL-4 compared to females following intravenous 7DW8-5 administration. Additionally, unlike in female mice, 7DW8-5 did not improve the vaccine efficacy against sporozoite challenge in prime-and-trap vaccinated male mice. Our findings highlight the importance of including both female and male sexes in experimental adjuvant studies.

An Efficient and Concise Synthesis of α-Galactosylceramide

A concise and stereoselective synthesis of α-galactosylceramide (α-GalCer) is described. The key features of the synthetic strategy are the use of a phytosphingosine in which the amine is masked as a tetrachlorophthalimide and the diol as an isopropylidene acetal, and the galactosyl donor is protected as a 4,6-benzylidene to improve the α selectivity of the glycosylation reaction. The pattern of protecting groups on the donor and the acceptor have proven to give an excellent match of reactivity, allowing the glycosylation reaction to take place stereoselectively. The overall synthesis gave α-GalCer in good yields and in few steps.

Chemical Strategies to Boost Cancer Vaccines

Personalized cancer vaccines (PCVs) are reinvigorating vaccine strategies in cancer immunotherapy. In contrast to adoptive T-cell therapy and checkpoint blockade, the PCV strategy modulates the innate and adaptive immune systems with broader activation to redeploy antitumor immunity with individualized tumor-specific antigens (neoantigens). Following a sequential scheme of tumor biopsy, mutation analysis, and epitope prediction, the administration of neoantigens with synthetic long peptide (SLP) or mRNA formulations dramatically improves the population and activity of antigen-specific CD4+ and CD8+ T cells. Despite the promising prospect of PCVs, there is still great potential for optimizing prevaccination procedures and vaccine potency. In particular, the arduous development of tumor-associated antigen (TAA)-based vaccines provides valuable experience and rational principles for augmenting vaccine potency which is expected to advance PCV through the design of adjuvants, delivery systems, and immunosuppressive tumor microenvironment (TME) reversion since current personalized vaccination simply admixes antigens with adjuvants. Considering the broader application of TAA-based vaccine design, these two strategies complement each other and can lead to both personalized and universal therapeutic methods. Chemical strategies provide vast opportunities for (1) exploring novel adjuvants, including synthetic molecules and materials with optimizable activity, (2) constructing efficient and precise delivery systems to avoid systemic diffusion, improve biosafety, target secondary lymphoid organs, and enhance antigen presentation, and (3) combining bioengineering methods to innovate improvements in conventional vaccination, "smartly" re-educate the TME, and modulate antitumor immunity. As chemical strategies have proven versatility, reliability, and universality in the design of T cell- and B cell-based antitumor vaccines, the union of such numerous chemical methods in vaccine construction is expected to provide new vigor and vitality in cancer treatment.

Synthetic preparation and immunological evaluation of β-mannosylceramide and related N-acyl analogues

The synthesis of the invariant natural killer (iNK) T cell agonist β-mannosylceramide along with a series of fatty amide analogues is reported. Of the six β-glycosylation protocols investigated, the sulfoxide methodology developed by Crich and co-workers proved to be the most effective where the reaction of a mannosyl sulfoxide and phytosphingosine derivative gave a key glycolipid intermediate as a 95 : 5 mixture of β- to α-anomers in high yield. A series of mannosyl ceramides were evaluated for their ability to activate D32.D3 NKT cells and induce antitumour activity.

Formal Synthesis of Indolizidine and Quinolizidine Alkaloids from Vinyl Cyclic Carbonates

Cyclic carbonates have long been considered relatively inert molecules acting as protecting groups in complex multistep synthetic routes. This study shows that a concise, yet modular synthesis of indolizidine and quinolizidine alkaloids can be developed from vinyl-substituted cyclic carbonate (VCC) intermediates. Through a highly stereoselective palladium-catalyzed allylic alkylation reaction, these alkaloid motifs can be assembled in four synthetic and only two column purification steps. The combined results help to further advance functionalized cyclic carbonates as useful and reactive intermediates in natural product synthesis.