From Polymer to Size‐Defined Oligomers: A Step Economy Process for the Efficient and Stereocontrolled Construction of Chondroitin Oligosaccharides and Biotinylated Conjugates Thereof: Part 1

Abstract

Controlled acid hydrolysis of polymeric chondroitin sulfate of bovine origin afforded in good yield a basic disaccharide fragment that was used for the first time as a starting material for the expeditious preparation of a set of building blocks that in turn act as versatile synthons for the efficient and stereocontrolled construction of a collection of size-defined chondroitin oligomers (from di- to octasaccharides). This step economy process allows their preparation as reducing species, fitted with a fluorophore, or as biotinylated conjugates; all useful tools for the preparation of microarrays, or as probes for the study of the biosynthesis of chondroitin sulfate.

Efficient and Stereocontrolled Construction of Homo‐ and Heterogeneously 4‐ and 6‐Sulfated Biotinylated Chondroitin Oligomers

“…Low-resolution mass spectra were obtained on a Perkin-Elmer SCIEX API 300 spectrometer operating in the ion-spray mode or on a Micromass Quattro Ultima spectrometer equipped with a Z-spray ionization source operating in the negative mode. HRMS were obtained from the Cen- A mixture of TFA/water (3:1, 1.8 mL) was added at 0°C to a solution of 1 [8] (516 mg, 0.57 mmol) in CH 2 Cl 2 (5 mL). The reaction mixture was stirred for 1 h at 0°C, then was diluted with CH 2 Cl 2 , washed with a saturated aqueous solution of NaHCO 3 …”

“…They could be prepared from 1 through selective protections on the GlcA unit to allow further elongation at the non-reducing end. However, they were more efficiently prepared from disaccharide derivative 13 (Scheme 2), which was easily available in 12 steps from the natural polymer, [8] and start- ing from a sequence similar to that achieved above could be applied. In 13, the NAP group [15] was conveniently used as a temporary protection at the anomeric center of the dgalactosamine units.…”

“…The 1 H and 13 C NMR spectra for 9 and 10 showed high purity and were in full agreement with the expected structures. Finally, catalytic hydrogenation of 9 and 10 with 10 % palladium on carbon in water gave the intermediate corresponding amines, which were further treated with N-hydroxysuccinimidoyl 6-(biotinylamido)hexanoate [8] and triethylamine in DMF/water to afford, for the first time, after purification on Sephadex LH-20 in water, the target 4-(11) and 6-sulfated (12) biotinylated conjugates, respectively, in good yields. The structure and chemical purity of 11 and 12 were readily established through 1 H and 13 C NMR spectroscopy (see the Supporting Information).…”

“…To this end, we took advantage of the availability of the disaccharide derivative 1 (Scheme 1), which was easily prepared on a multigram scale in eight steps from natural CS polymer. [8] The N-trichloroacetyl group, a powerful stereocontrolling auxiliary for the synthesis of 1,2-trans-2-amino-2-deoxyglycosides, [10] was systematically employed along this work for the preparation of β-galactosaminides. The protective group pattern in 1 allowed fast access to O-4 and O-6 at the GalNAc moiety and further possible biotinylation at the reducing end.…”

“…We previously reported a step-economical process for the chemical synthesis of size-defined chondroitin oligomers by semisynthesis starting from a commercially available natural CS polymer, [7] and the application of this strategy for the stereocontrolled construction of non-sulfated and biotinylated chondroitin oligomers, [8] as well as those of all known variants of CS. [9] Within a program devoted to the study of the biosynthetic pathways of CS chains in relation to osteoarthritis, we report herein an efficient and stereocontrolled construction of homo-and heterogeneously 4-and 6-sulfated chondroitin oligomers as their biotinylated conjugates, which are useful molecules as probes for studying the initiation of the polymerization of CS chains and the role of sulfotransferases involved in CS chain construction in cartilage.…”