Synthesis of serine-based glycolipids as potential TLR4 activators

Abstract

A new series of monosaccharide-based glycolipids devoid of phosphate groups and with two lipid chains were rationally designed by varying the lipid chain lengths and saccharide structure of a α-GalCer-derived lead compound (CCL-34) that is a potent TLR4 agonist. The NF-κB activity of a 60-membered galactosyl serine-based synthetic library containing compounds with various lipid chain lengths was measured in a HEK293 cell line that stably expressed human TLR4, MD2, and CD14 (293-hTLR4/MD2-CD14). The results showed that the optimal carbon chain lengths for the lipid amine and fatty acid to activate TLR4 were 10-11 and 12, respectively. Evaluation of a 20-membered synthetic glycosyl serine-based lipid library containing compounds with various saccharide moieties and fixed lipid chain lengths revealed that the galactose moiety in CCL-34 could be replaced by glucose without loss of activity (CCL-34-S3 and CCL-34-S16). Changing the orientation of the anomeric glycosidic bond of CCL-34 resulted in a complete loss of activity (β-CCL34). Surprisingly, a change in configuration of the anomeric glycosidic bond in a glucosyl glycolipid is tolerable (CCL-34-S14). Another noteworthy observation is that the activity of a l-fucosyl derived glycolipid (CCL-34-S13) was comparable to that of CCL-34. In sum, this study determines the structural features that are crucial for an optimal TLR4-stimulating activity. It also provides several molecules with immunostimulating potential.

Characterization of Meiothermus taiwanensis Galactokinase and its Use in the One‐Pot Enzymatic Synthesis of Uridine Diphosphate‐Galactose and the Chemoenzymatic Synthesis of the Carbohydrate Antigen Stage Specific Embryonic Antigen‐3

“…The pentasaccharide precursor of 2b was constructed by coupling protected Gb3 (6) with disaccharide 7 (disconnection 1). Compound 7 could be quickly assembled by borinate ester-assisted selective glycosylation between building block 8 and the galactosyl donor 9 [37] (disconnection 2). In addition, an aminohexanyl spacer was incorporated for conjugation with a carrier protein.…”

Toll-like Receptor 4 (TLR4) Modulation by Synthetic and Natural Compounds: An Update

“…While the anomeric α-configuration is essential to the biological activity, the galactose moiety can be replaced by other monosaccharides (α-fucose, α- or β-glucose, α-galacturonic acid) retaining the TLR4-stimulating activity, as assessed by experiments on HEK cells stably transfected with TLR4, MD-2 and CD14 receptors. 30 The antitumor potential of TLR4 agonist 7 was studied: macrophages activated by the synthetic ceramide induced cancer cell death via the apoptotic pathway and treatment with 7 suppressed tumor growth and increased the survival rate in TLR4-functional C3H/HeN mice but not in TLR4-defective C3H/HeJ mice. 31 Other natural and synthetic α-GalCer are known to possess immunostimulant activities, molecule KRN7000 32 (Figure 3), that is a simplified analogue of glycosphingolipids of marine origin is capable of activating natural killer T (NKT) cells.…”

CCL-34, a synthetic toll-like receptor 4 activator, modulates differentiation and maturation of myeloid dendritic cells

“…The TLR4 activators reported to elicit immunity of DC include glucopyranosyl lipid A [ 13 ], C. nebularis lectin [ 14 ], OM-174 [ 15 ], OK-432 [ 16 ] and poly-gamma-glutamate [ 17 ]. Among currently identified TLR4 activators, CCL-34 is advantageous due to its defined structure and well-established synthesis procedure [ 18 ]. Given that CCL34 could activate TLR4 to promote macrophage function [ 11 ] and DC maturation, CCL34 may serve as a potential immune modulator for immunotherapy, such as adjuvant for vaccines.…”