Synthetic and Immunological Studies of Mycobacterial Lipoarabinomannan Oligosaccharides and Their Protein Conjugates

Abstract

Lipoarabinomannan (LAM) is one of the major constituents of the Mycobacterium tuberculosis cell wall and an attractive molecular scaffold for antituberculosis drug and vaccine development. In this paper, a convergent strategy was developed for the synthesis of LAM oligosaccharides with an α-1,2-linked dimannopyranose cap at the nonreducing end. The strategy was highlighted by efficient coupling of separately prepared nonreducing end and reducing end oligosaccharides. Glycosylations were mainly achieved with thioglycoside donors, which gave excellent yields and stereoselectivity even for reactions between complex oligosaccharides. The strategy was utilized to successfully synthesize tetra-, hepta-, and undecasaccharides of LAM from d-arabinose in 10, 15, and 14 longest linear steps and 7.84, 7.50, and 2.59% overall yields, respectively. The resultant oligosaccharides with a free amino group at their reducing end were effectively conjugated with carrier proteins, including bovine serum albumin and keyhole limpet hemocyanin (KLH), via a bifunctional linker. Preliminary immunological studies on the KLH conjugates revealed that they could elicit robust antibody responses in mice and that the antigen structure had some influence on their immunological property, thus verifying the potential of the oligosaccharides for vaccine development and other immunological studies.

Expedient synthesis of the heneicosasaccharyl mannose capped arabinomannan of the Mycobacterium tuberculosis cellular envelope by glycosyl carbonate donors

“…19–27,44 A recent investigation by Guo's group verified the synthetic and immunological potential of protein conjugated ManLAM fragments. 28 However, far too little attention has been paid to synthesizing the large oligomers in ManLAM. The main aim of the current research has therefore been to synthesize naturally occurring large oligosaccharide portions of ManLAM such as arabinomannan 1 (Fig.…”

Size Matters: Chemical Synthesis of a Homogenous Arabinogalactan 92‐mer

“…The cell‐wall oligosaccharides produced by bacteria are another example of branched and complex oligosaccharide structures. Such oligomers are composed of repeating units of furanose and, because the structures are unique to each bacterial strain, they have been used as epitopes for vaccines against bacterial pathogens . The critical question is: which fragments of an oligosaccharide and how many repeating units are sufficient to elicit robust immune response?…”

Preparation and in vivo evaluation of glyco-gold nanoparticles carrying synthetic mycobacterial hexaarabinofuranoside

“…A number of bacterial glycans [1,2] are specific markers for the detection and the serological identification of microorganisms [3][4][5] and are widely used as antigenic components of vaccines [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. The use of gold nanoparticles (GNPs) [24][25][26] as carriers for glyco-epitopes is becoming an important alternative [15, to the traditional conjugation with proteins, synthetic polymers and other carriers [15,17,38,[49][50][51][52][53][54][55].…”

“…Lipoarabinomannan (LAM) and the related arabinogalactan (AG) are two major structural components of the M. tuberculosis cell wall. Previous studies revealed that LAM and especially its terminal oligosaccharide fragments, conjugated with proteins [7,10,19] or monophosphoryl lipid A [23], are attractive targets for the development of carbohydrate-based anti-TB vaccines [7,10,19,23,65,66].…”