Naphthyl Thio‐ and Carba‐xylopyranosides for Exploration of the Active Site of β‐1,4‐Galactosyltransferase 7 (β4GalT7)

Abstract

Xyloside analogues with substitution of the endocyclic oxygen atom by sulfur or carbon were investigated as substrates for β-1,4-galactosyltransferase 7 (β4GalT7), a key enzyme in the biosynthesis of glycosaminoglycan chains. The analogues with an endocyclic sulfur atom proved to be excellent substrates for β4GalT7, and were galactosylated approximately fifteen times more efficiently than the corresponding xyloside. The 5a-carba-β-xylopyranoside in the d-configuration proved to be a good substrate for β4GalT7, whereas the enantiomer in the l-configuration showed no activity. Further investigations by X-ray crystallography, NMR spectroscopy, and molecular modeling provided a rationale for the pronounced activity of the sulfur analogues. Favorable π-π interactions between the 2-naphthyl moiety and a tyrosine side chain of the enzyme were observed for the thio analogues, which open up for the design of efficient GAG primers and inhibitors.

Fluorescently labeled xylosides offer insight into the biosynthetic pathways of glycosaminoglycans

“…Glycosylation was first attempted using the peracetylated thioxyloside in a similar fashion as the other targets with BF 3 ·OEt 2 as the promoter, without success. Previous glycosylations using this donor, 19,36 have involved aromatic, rather than aliphatic, thiols as acceptors, which could explain the low reactivity. Instead, we used the 2,3,4-tri- O -acetyl-5-thio-α- d -xylopyranosyl bromide 37 (23), and ZnO–ZnCl 2 as the promoter system in a MeCN-toluene mixture 38 along with a Boc-protected linker.…”

“…The later analog has been shown to be a good substrate for b4GalT7. 19 Synthesis of targets 5-8 was performed using conventional carbohydrate synthetic methods (Scheme 1a), starting from peracetylated D-xylose (10) and commercially available, suitably protected linkers. Glycosylation using BF 3 $OEt 2 in MeCN, with Cbzprotected amino alcohols furbished compounds 11, 14, 17, and 20.…”

“…1 H NMR (400 MHz, MeOD) d 5.23 (t, J ¼ 9.2 Hz, 1H, H-3), 4.96-4.92 (m, 1H, H-4)*, 4.86 (dd, J ¼ 9.3, 7.4 Hz, 1H, H-2), 4.60 (d, J ¼ 7.4 Hz, 1H, H-1), 4.08 (dd, J ¼ 11.7, 5.4 Hz, 1H, H-5 eq ), 3.88 (dt, J ¼ 9.8, 5.7 Hz, 1H, O-CH 2 -), 3.61 (dt, J ¼ 9.8, 5.7 Hz, 1H O-CH 2 -), 3.47 (dd, J ¼ 11.7, 9.8 Hz, 1H, H-5 ax ), 2.95 (t, J ¼ 6.8 Hz, 2H, CH 2 -N), 2.06 (s, 3H, Ac), 2.03 (s, 3H, Ac), 2.02 (s, 3H, Ac), (m, 4H, -CH 2 -CH 2 -). 13 4-(6,8-Diuoro-7-hydroxycoumarin-3-carboxamido)butyl 2,3,4-tri-O-acetyl-b-D-xylopyranoside (19). 18 (41.4 mg, 0.121 mmol) was subjected to procedure C to yield 19 as a yellow amorphous solid (41.5 mg, 0.0698 mmol, 58%) [a] 25 D 35.2 (c 0.39, MeCN).…”

“…18 To study the biosynthesis, and search for a GAGosome, a uorescently labeled xyloside that functions as a GAG primer would be highly valuable. [19][20][21] For this approach to be successful, the xyloside must be able to rst permeate through the cell membrane and then be able to initiate GAG-synthesis.…”

Chemoenzymatic Synthesis of Glycopeptides Bearing Galactose–Xylose Disaccharide from the Proteoglycan Linkage Region

“…This knowledge has led to the fascinating utility of xylosides as a tool to prime cellular synthesis of glycosaminoglycans and modulate cellular functions. In addition, various xyloside analogues have been synthesized to probe the catalytic sites of β4GalT7. − However, to the best of our knowledge, β4GalT7 has not been explored for glycopeptide synthesis. Herein, we report that human β4GalT7 enzyme can be utilized to catalyze the formation of native β4GalT7 PGs.…”