An efficient methodf or a-selective sialylation, based on ap re-activated5 -N,4-O-carbamate thiosialoside donor using p-TolSCl/AgOTf as reagents, is described. The strategy is further expandedt oar ange of sugars. Amechanism is proposed and validated using experimental evidence. The utility of the method is demonstrated by the total synthesis of gangliosides Hp-s1 1,D SG-A 2 and their analogues, 2a-2c.T he neuritogenic activity of the final compounds is determined on SH-SY5Y cells.

Ganglioside Hp-s1 is isolated from the ovary of sea urchin Diadema setosum. It exhibited better neuritogenic activity than GM1 in pheochromocytoma 12 cells. To explore the roles of glucosyl moiety of Hp-s1 in contributing to the neurogenic activity, we developed feasible procedures for synthesis of Hp-s1 analogues (2a-2f). The glucosyl moiety of Hp-s1 was replaced with α-glucose, α-galactose, β-galactose, α-mannose, and β-mannose, and their biological activities on SH-SY5Y cells and natural killer T (NKT) cells were evaluated. We found that the orientation of C-2 hydroxyl group at glucosyl moiety of Hp-s1 plays an important role to induce neurite outgrowth of SH-SY5Y cells. Surprisingly, compound 2d could activate NKT cells to produce interleukin 2, although it did not show great activity on neurite outgrowth of SH-SY5Y cells. In general, the Hp-s1 might be considered as a lead compound for the development of novel drugs aimed at modulating the activity of neuronal cells.

The complete synthesis of the ganglioside Hp-s1 (1) is described in 10 steps.

Invariant natural killer T (iNKT) cells play an important role in the immune system and the previous discovery of their activation by α‐galactosyl ceramide (α‐GalCer) has provided a new armamentarium for immune modulation via stimulation of iNKT cells. Our recent findings showed that N‐methylated α‐GalCer (NCH3‐α‐GalCer) has little activity in iNKT cell stimulation. In this study, we used computer simulation to elucidate the negative impact of a methyl group at the amide moiety of α‐GalCer on the interaction with CD1d. Based on computer modeling of the ternary complex of CD1d, glycolipid and TCR of NKT, we hypothesized that OH substitution at the C‐5 of the phytosphingosine chain of NCH3‐α‐GalCer might form a hydrogen bond with CD1d and stabilize the CD1d‐glycolipid complex. In addition, the stereochemical configuration at the C‐3 and C‐5 might play an important role in the activity of NCH3‐α‐GalCer. We accordingly generated NCH3‐α‐GalCer analogues containing OH substitution at the C‐5 with different stereochemical configurations of OH at the C‐3 and C‐5 of phytosphingosine chain (2 a‐2 d) by a direct and simple synthetic strategy, including coupling pyrano‐reducing sugars with D‐galactosyl iodide, functional group transformations and installing a methyl group at the amide group of α‐GalCer. Activities of these analogues were evaluated in vitro with CD1d‐expressing A20 cells and murine NK1.2 cells and in vivo in C57BL/6 mouse. As compared to NCH3‐α‐GalCer (2), analogues 2 a showed significantly increased production of IL‐2 in vitro and various cytokines, including IL‐4 and IL‐2, in vivo. In addition, the (3S)‐OH (2 a and 2 d) showed better activities than those with (3R)‐OH (2 b and 2 c). These results suggested that addition of OH group at the C‐5 of phytosphingosine chain of α‐GalCer could restore the activity of NCH3‐α‐GalCer and that S configuration at the position C‐3 and C‐5 of the phytosphingosine chain could dictate their immunomodulatory activities. Above all, structure‐activity relationship analyses with in silico modeling can facilitate the design of NKT‐stimulatory glycolipids as immune‐modulating agents.

The Wittig reaction of the pyrano-type reducing sugars undergoes an unexpected formation of dienes through the elimination of a benzyloxy group in the presence of t-BuOK. LiHMDS is used rather than tBuOK to prevent alcohol elimination in the same sugar derivatives. Collectively, t-BuOK has unusual functions in the Wittig reaction that correspond with other bases such as LiHMDS, NaH, and n-BuLi. This unusual function of t-BuOK showed that a unique 4-deoxy-5-hydroxyl analogue 2 of a-galactosyl ceramide was formed exclusively.