Adjuvants are components of vaccine that enhance the specific immune response against co-inoculated antigens. Recently, we reported the characterization of a synthetic sulfolipid named Sulfavant A ( 1 ) as a promising candidate of a novel class of molecular adjuvants based on the sulfoquinovosyl-diacylglycerol skeleton. Here, we report an improved synthesis of the sulfolipid scaffold, as well as the preparation of two analogs named Sulfavant-S ( 2 ) and Sulfavant-R ( 3 ) with enhanced property to modulate master immune targets such as human dendritic cells (DCs). According to the present approach, synthesis of 1 is reduced from 14 to 11 steps with nearly triplication of the overall yield (11%). The new members 2 and 3 elicit DC maturation at a concentration of 10 nM, which is 1000 times more potent than the parent molecule 1 . Analysis of dynamic light scattering indicates self-assembly of Sulfavants and formation of colloidal particles with a small hydrodynamic radius (50 nm) for the epimers 2 and 3 and a larger radius (150 nm) for 1 . The colloidal aggregates are responsible for the bell-shaped dose–response curve of these products. We conclude that the particle size also affects the equilibrium with free monomers, thus determining the effective concentration of the sulfolipid molecule at the cellular targets and the different immunological efficacy of 1–3 . Sulfavants ( 1–3 ) do not show in vitro cytotoxicity at concentrations 10 5 higher than the dose that triggers maximal immune response, thus predicting a low level of toxicological risk in their formulation in vaccines.

Vaccines play a primary role in the protection of human health by preventing infectious and chronic diseases. Recently we have reported 1,2-O-distearoyl-3-O-β-d-sulfoquinovosylglycerol (β-SQDG18), here named Sulfavant A (1), which shows promising properties as a new molecular adjuvant in in vitro and in vivo tests. In the present manuscript, we provide full details about a synthetic strategy for the preparation of 1, including a discussion of chemical determinants of the activity and the major technical hurdles we faced during the study. Synthesis of Sulfavant A (1) is achieved by a versatile procedure based on a trichloroacetimidate methodology and peracetate sugar precursors. The final design opens possibilities for the preparation of a series of interesting analogs for further pharmacological optimization and development, including derivatives containing different saturated and polyunsaturated fatty acids (e.g., 17 and 22).

Objective The immune response arises from a fine balance of mechanisms that provide for surveillance, tolerance, and elimination of dangers. Sulfavant A (SULF A) is a sulfolipid with a promising adjuvant activity. Here we studied the mechanism of action of SULF A and addressed the identification of its molecular target in human dendritic cells (hDCs). Methods Adjuvant effect and immunological response to SULF A were assessed on DCs derived from human donors. In addition to testing various reporter cells, target identification and downstream signalling was supported by a reverse pharmacology approach based on antibody blocking and gene silencing, crosstalk with TLR pathways, use of human allogeneic mixed lymphocyte reaction. Results SULF A binds to the Triggering Receptor Expressed on Myeloid cells-2 (TREM2) and initiates an unconventional maturation of hDCs leading to enhanced migration activity and up-regulation of MHC and co-stimulatory molecules without release of conventional cytokines. This response involves the SYK-NFAT axis and is compromised by blockade or gene silencing of TREM2. Activation by SULF A preserved the DC functions to excite the allogeneic T cell response, and increased interleukin-10 release after lipopolysaccharide stimulation. Conclusion SULF A is the first synthetic small molecule that binds to TREM2. The receptor engagement drives differentiation of an unprecedented DC phenotype (homeDCs) that contributes to immune homeostasis without compromising lymphocyte activation and immunogenic response. This mechanism fully supports the adjuvant and immunoregulatory activity of SULF A. We also propose that the biological properties of SULF A can be of interest in various physiopathological mechanisms and therapies involving TREM2.

Recently, we reported the promising activity of a novel class of sulfoquinovosyl-diacylglycerols named Sulfavants as molecular vaccine adjuvants. Herein, we describe a modified and improved chemical synthesis of the lead product Sulfavant A (1), with the aim to produce from milligrams to 10 g of the pure compound that is necessary for the preclinical development. Starting from the versatile synthesis based on the trichloroacetimidate methodology, up-scaled preparation of Sulfavant A (1) was achieved in 11 steps by elimination and modification of those reactions that negatively affected the overall yield by the previous procedure. The novel strategy gave 17% overall yield of the target compound 1 and also paved the way for the gram-scale preparation of a wide range of other charged and neutral glycoglycerolipids.