Removal of benzylidene acetal and benzyl ether in carbohydrate derivatives using triethylsilane and Pd/C

Abstract

SummaryClean deprotection of carbohydrate derivatives containing benzylidene acetals and benzyl ethers was achieved under catalytic transfer hydrogenation conditions by using a combination of triethylsilane and 10% Pd/C in CH3OH at room temperature. A variety of carbohydrate diol derivatives were prepared from their benzylidene derivatives in excellent yield.

Concise Synthesis of a Pentasaccharide Repeating Unit Corresponding to the O‐Antigen of Salmonella Enterica O51

“…Spectral analysis of compound 13 was in full agreement with its formation [δ 5.62 (d, J =8.0 Hz, H‐1 E ), 5.15 (d, J =8.5 Hz, H‐1 B ), 5.13 (br s, H‐1 C ), 4.78 (d, J =8.0 Hz, H‐1 D ), 4.44 (d, J =3.0 Hz, H‐1 A ) in 1 HNMR and δ 101.5 (C‐1 D ), 99.8 (2 C, C‐1 B , C‐1 E ), 98.7 (C‐1 C ), 97.3 (C‐1 A ) in 13 CNMR spectra]. A set of reactions were carried out for the functional group transformations in compound 13 , which include (a) treatment with thioacetic acid to convert azido group to acetamido group; (b) treatment with hydrazine monohydrate to remove phthalimido group to give free amine; (c) treatment with acetic anhydride in pyridine to acetylate the free amine and hydroxyl groups; (d) catalytic transfer hydrogenation in the presence of a combination of triethylsilane and 20 % Pd(OH) 2 ‐C and (e) treatment with sodium methoxide to give deprotected pentasaccharide 1 in 52 % over all yield. NMR spectral analysis of compound 1 unambiguously confirmed its formation with appropriate stereochemistry around the glycosyl linkages [signals at δ 5.48 (d, J =4.0 Hz, H‐1 C ), 4.98 (d, J =3.5 Hz, H‐1 A ), 4.76 (d, J =8.5 Hz, H‐1 E ), 4.61 (d, J =8.0 Hz, H‐1 B ), 4.49 (d, J =8.0 Hz, H‐1 D ) in 1 H NMR and δ 104.7 (C‐1 D ), 102.6 (C‐1 E ), 101.1 (C‐1 B ), 98.2 (C‐1 A ), 97.1 (C‐1 C ) in 13 CNMR spectra] (Scheme ).…”

Convergent Synthesis and Conformational Analysis of the Hexasaccharide Repeating Unit of the O‐Antigen of Shigella flexneri Serotype 1d

“…s, 1 D ‐H) in the 1 H NMR spectrum, and δ = 99.9 (C‐1 D ), 97.9 (2 C, C‐1 A , C‐1 C ), 97.2 (C‐1 E ), 94.6 (C‐1 B ), 94.5 (C‐1 F ) in the 13 C NMR spectrum] and the J C‐1,1‐H coupling constants30,31 in the gated 1 H‐coupled 13 C NMR spectrum (154.0, 165.0, 171.0, 165.0, 171.5, and 171.5 Hz) confirmed the presence of five α glycosidic linkages and one β linkage. Compound 16 was subjected to a sequence of deprotection reactions comprising (a) removal of the N ‐phthaloyl group using ethylenediamine,34 followed by acetylation using acetic anhydride and pyridine; (b) catalytic transfer hydrogenation35 using a combination of triethylsilane and Pd/C (10 %) for the removal of the benzyl ethers and the benzyloxycarbonyl (Cbz) protecting group, and (c) removal of the O ‐acetyl groups using sodium methoxide, to give deprotected hexasaccharide 1 as its 2‐aminoethyl glycoside in 54 % overall yield. The product was passed through a column of LH‐20 Sephadex using CH 3 OH/H 2 O (4:1) as eluent to give pure compound 1 .…”

Expedient synthesis of a pentasaccharide related to the O-specific polysaccharide of Escherichia coli O117:K98:H4 strain

“…Slowly raising the reaction temperature in the reaction vessel initiated the hydrolysis (HClO 4 -SiO 2 ) of the PMB group and produced the desired tetrasaccharide acceptor. 30 The pentasaccharide derivative 13 was subjected to a sequence of reactions consisting of (a) treatment with hydrazine hydrate, 31 followed by acetylation using acetic anhydride and pyridine for the conversion of phthalimido group into acetamido group; (b) treatment with thioacetic acid 32 to convert azido group to acetamido group; (c) removal of benzyl ethers and benzylidene acetal under a catalytic transfer hydrogenation condition using triethylsilane and 20% Pd(OH)-C, 33 and nally and (d) saponication using sodium methoxide 34 to furnish desired pentasaccharide PMP glycoside 1 in 52% over all yield. The formation of compound 13 was unambiguously conrmed by NMR spectroscopy [signals at d 5.52 (d, J ¼ 7.…”