Synthesis of Branched Trehalose Glycolipids and Their Mincle Agonist Activity.

The macrophage inducible C-type lectin (Mincle) is a pattern recognition receptor that recognizes trehalose dimycolate (TDM), and trehalose dibehenate (TDB) and related trehalose diesters, and thus represents a promising target for the development of vaccine adjuvants based on the trehalose glycolipid scaffold. To this end, we report on the synthesis of a series of long-chain α-branched, β-modified trehalose monoesters and diesters to explore how glycolipid structure affects signaling through Mincle. Key steps in our synthetic strategy include a Fráter-Seebach α-alkylation to install the C20 aliphatic lipid on a malic acid derivative, and the formation of a β,γ-epoxide as an intermediate from which modifications to the β-position of the lipid can be made. Biological evaluation of the derivatives using nuclear factor of activated T cells (NFAT)-green fluorescent protein (GFP) reporter cell lines expressing mMincle or hMincle revealed that the hMincle agonist activity of all diesters was superior to that of the current lead trehalose glycolipid adjuvant TDB, while the activity of several monoesters was similar to that of their diester counterparts for mMincle, but all showed reduced hMincle agonist activity. Taken together, diesters 2d-g are thus potent Mincle agonists and promising vaccine adjuvants.