Preactivation‐Based, One‐Pot Combinatorial Synthesis of Heparin‐like Hexasaccharides for the Analysis of Heparin–Protein Interactions

Abstract

Heparin (HP) and heparan sulfate (HS) play important roles in many biological events. Increasing evidence has shown that the biological functions of HP and HS can be critically dependent upon their precise structures, including the position of the iduronic acids and sulfation patterns. However, unraveling the HP code has been extremely challenging due to the enormous structural variations. To overcome this hurdle, we investigated the possibility of assembling a library of HP/HS oligosaccharides using a preactivation-based, one-pot glycosylation method. A major challenge in HP/HS oligosaccharide synthesis is stereoselectivity in the formation of the cis-1,4-linkages between glucosamine and the uronic acid. Through screening, suitable protective groups were identified on the matching glycosyl donor and acceptor, leading to stereospecific formation of both the cis-1,4- and trans-1,4-linkages present in HP. The protective group chemistry designed was also very flexible. From two advanced thioglycosyl disaccharide intermediates, all of the required disaccharide modules for library preparation could be generated in a divergent manner, which greatly simplified building-block preparation. Furthermore, the reactivity-independent nature of the preactivation-based, one-pot approach enabled us to mix the building blocks. This allowed rapid assembly of twelve HP/HS hexasaccharides with systematically varied and precisely controlled backbone structures in a combinatorial fashion. The speed and the high yields achieved in glycoassembly without the need to use a large excess of building blocks highlighted the advantages of our approach, which can be of general use to facilitate the study of HP/HS biology. As a proof of principle, this panel of hexasaccharides was used to probe the effect of backbone sequence on binding with the fibroblast growth factor-2 (FGF-2). A trisaccharide sequence of 2-O-sulfated iduronic acid flanked by N-sulfated glucosamines was identified to be the minimum binding motif and N-sulfation was found to be critical. This provides useful information for further development of more potent compounds towards FGF-2 binding, which can have potential applications in wound healing and anticancer therapy.

Uncovering Biphasic Catalytic Mode of C5-epimerase in Heparan Sulfate Biosynthesis

“…A cost-effective method to prepare synthetic heparin is desirable. Using HS biosynthetic enzymes, we developed a chemoenzymatic approach to synthesize structurally defined HS and heparin oligosaccharides in high efficiency, which significantly expands the synthetic capability by a purely chemical approach (4,5).…”

Glyco-Nanomaterials: Translating Insights from the “Sugar-Code” to Biomedical Applications

“…Mousa and coworkers reported the synthesis of heparin coated AuNPs (HP-AuNPs) [121]. Heparin is a class of naturally occurring polysaccharides, which can inhibit basic fibroblast growth factor-2 induced angiogenesis [146]. The HP-AuNPs were found to have significantly higher anti-angiogenesis efficacy compared with the corresponding Glc-AuNPs.…”

Chemical Synthesis of a Heparan Sulfate Glycopeptide: Syndecan‐1

“…Although the a-glycosyl linkage between GlcN and IdoA was formed stereospecifically using monosaccharide building blocks in our previous study, [10] the coupling between 2 and 3 failed to yield the desired heptasaccharide and donor decomposition products were isolated as the major side products. Varying the protective groups on 2 and 3 did not improve the situation.…”

“…Previously, when the PMB group was used to mask the 6O-position of the glycosyl donors, the electron-rich PMB moiety participated in the reaction by forming a 1,6-anhydro sugar, thus shutting down the desired glycosylation. [10] To avoid this side reaction, the PMB group in 12 was replaced by a TBDPS group with subsequent deprotection/protection sequences, thus generating the disaccharide acceptor 13. Coupling of the idosyl thioglycoside 14 with 13 produced the ABC trisaccharide 7 (Scheme 1 B).…”