Chemical Synthesis of the Major Constituents ofSalmonella MinnesotaMonophosphoryl Lipid A

3-O-Desacyl Monophosphoryl Lipid A Derivatives: Synthesis and Immunostimulant Activities

“…Koenigs−Knorr coupling of chlorides 12a − f with glycosyl acceptors 7a − f was effected in the presence of silver triflate to give exclusively the β-disaccharides 13a − f . The β-(1→6) linkage was assured by 300 MHz 1 H− 1 H COSY experiments and by analogy with synthetic 2 . It is noteworthy that this silver-promoted glycosylation with N -Troc-protected 2-amino-2- deoxyglucopyranosyl chlorides proceeds in 70−80% yield at room temperature with only a slight excess (1.1 equiv) of the glycosyl donor 12 , whereas the corresponding glycosyl bromide/Hg(CN) 2 protocol 17 requires a larger excess of the (less-stable bromide) donor and elevated temperatures to achieve comparable yields (see also preparation of 16f in Experimental Section).…”

“…The target MLA derivatives 3a − f were prepared in a highly convergent manner (Schemes and ) from the known benzyl and 2-(trimethylsilyl)ethyl (TMSEt, SE) β-glycosides 4 and 8 , respectively, and ( R )-3- n -alkanoyloxytetradecanoic acids 5a − f 15 (Chart ). Our strategy, based on our recently reported total synthesis of the major constituents (e.g., compound 2 ) of S. minnesota MPL, utilizes the N -2,2,2-trichloroethoxycarbonyl (Troc) method 17,18 and silver ion catalysis 18 to assemble the key β-(1→6) disaccharide intermediates 13a − f in a stereospecific manner from glycosyl chlorides 12a − f and diols 7a − f . Remarkably, very few silver-promoted condensation reactions of N -Troc- and other N -alkoxycarbonyl-protected 2-amino-2-deoxyglycosyl chlorides have been reported. , The TMSEt group was selected for anomeric protection in the synthesis of the glycosyl chlorides 12a − f because of the facility with which it can be converted directly into 1-chloro derivatives …”

MPL Adjuvant Contains Competitive Antagonists of Human TLR4

“…Acyl chains in the PHAD synthetics are uniformly C14 in length, whereas the Lipid A synthetic has one secondary acyl chain that is C12. Individual components of MPL adjuvant ® were synthesized as described previously (18,19) as 3-O-desacyl-4′monophosphoryl lipid A congeners with varying numbers of acyl chains corresponding to the major components found in clinical-grade MPL adjuvant ® : hexa-acylated (hereafter referred to as ML6, 2:2:0:2 acyl chain configuration), penta-acylated (ML5A and ML5B, 2:2:0:1 and 1:2:0:2 acyl chain configurations, respectively), tetra-acylated (ML4A and ML4B, 1:2:0:1 and 0:2:0:2 acyl chain configurations, respectively), and tri-acylated (ML3, 0:2:0:1 acyl chain configuration) monophosphoryl lipid A. The MPL ® adjuvant synthetics reflect differences in acyl chain lengths of S. enterica Minnesota LPS in which the 2′-secondary acyl chain is C12, and the 2secondary acyl chain is C16 in length.…”

“…MPL ® adjuvant is a heterogeneous mixture of congeneric lipid A with 4′-phophoryl groups and varying numbers of acyl chains (10,13,14,(17)(18)(19), as summarized in Figure 4A. Figure 4B shows other synthetic Lipid A preparations used in our study, including E. coli chemotype PHAD and 3D-6A-PHAD, the latter of which is almost identical to the best known component of MPL ® , hexa-acyl ML6, by virtue of lacking a fatty acid at position 3 of the reducing half of the diglucosamine headgroup.…”

“…The complexity of the process used to manufacture MPL ® from LPS, needed to ensure it is both safety and functionality, generates multiple congeneric forms with anywhere from three to six acyl chains (10,13,14,(17)(18)(19)(20). The hexa-acylated species is generally highlighted when structures of MPL ® are published (21), even though it is not the most abundant (17) and the penta-acylated species is fully functional as an adjuvant in mice (17).…”