Abstract:The discovery of novel conditions for highly beta-stereoselective (>9 : 1) mannosylation of OH-2 of mannosides using a straightforward perbenzylthioglycoside donor has allowed ready assembly of beta-mannosyl oligosaccharides including the repeating trisaccharide motif of the O5 antigen of pathogen Klebsiella pneumoniae.
“…The α - linkage in d -mannosides was confirmed by the carbon-proton coupling constant ( 2 J C–H ) of the anomeric carbon by acquiring the non-decoupled 13 C NMR spectra. For example, the 2 J C–H is 167.9 Hz for the anomeric carbon of the d -mannose residue in compound 23 , which confirms that 23 is an α -mannoside since the 2 J C–H of the anomeric carbon for a β -mannoside is typically below 160 Hz [ 24 ]. Fig.…”
A series of novel 4β-triazole-podophyllotoxin glycosides were synthesized by utilizing the Click reaction. Evaluation of cytotoxicity against a panel of five human cancer cell lines (HL-60, SMMC-7721, A-549, MCF-7, SW480) using MTT assay shows that most of these compounds show weak cytotoxicity. It was observed that compound 16 shows the highest activity with IC50 values ranging from 2.85 to 7.28 μM, which is more potent than the control drugs etoposide and cisplatin against four of five cancer cell lines tested. Compound 16 is characterized with an α-d-galactosyl residue directly linked to the triazole ring and a 4′-OH group on the E ring of the podophyllotoxin scaffold. HPLC investigation of representative compound indicates that incorporation of a sugar moiety seems to improve the chemical stability of the podophyllotoxin scaffold.
“…The α - linkage in d -mannosides was confirmed by the carbon-proton coupling constant ( 2 J C–H ) of the anomeric carbon by acquiring the non-decoupled 13 C NMR spectra. For example, the 2 J C–H is 167.9 Hz for the anomeric carbon of the d -mannose residue in compound 23 , which confirms that 23 is an α -mannoside since the 2 J C–H of the anomeric carbon for a β -mannoside is typically below 160 Hz [ 24 ]. Fig.…”
A series of novel 4β-triazole-podophyllotoxin glycosides were synthesized by utilizing the Click reaction. Evaluation of cytotoxicity against a panel of five human cancer cell lines (HL-60, SMMC-7721, A-549, MCF-7, SW480) using MTT assay shows that most of these compounds show weak cytotoxicity. It was observed that compound 16 shows the highest activity with IC50 values ranging from 2.85 to 7.28 μM, which is more potent than the control drugs etoposide and cisplatin against four of five cancer cell lines tested. Compound 16 is characterized with an α-d-galactosyl residue directly linked to the triazole ring and a 4′-OH group on the E ring of the podophyllotoxin scaffold. HPLC investigation of representative compound indicates that incorporation of a sugar moiety seems to improve the chemical stability of the podophyllotoxin scaffold.
“…A disaccharide acceptor 7 was synthesized by stereoselective glycosylation of compound 2 and compound 3 in the presence of a combination of N ‐iodosuccinimide (NIS) and perchloric acid supported over silica (HClO 4 ‐SiO 2 ) followed by the removal of the O ‐benzoyl group . In order to synthesize a disaccharide thioglycoside derivative 9 containing a β‐D‐mannosidic linkage several attempts were made following the reports available in the literature . The best result in terms of yield and stereoselectivity was obtained following the report of Crich et al .…”
A convergent approach has been developed for the synthesis of the unique tetrasaccharide repeating unit corresponding to the O-polysaccharide of Salmonella enterica O41. The synthetic strategy involved generation of a b-D-mannopyranosidic linkage and an alpha-L-quinovasaminyl glycosidic linkage, which require special tuning in the reaction conditions to avoid the formation of undesired products. A stereoselective [2 + 2] block glycosylation strategy has been adopted for the synthesis of the target tetrasaccharide derivative. All glycosylations were highly stereoselective with satisfactory yield.
“…Successful approach to β‐1,2‐mannosides was also achieved by utilization of a perbenzylated thioglycoside donor activated with dimethyl disulfide/triflic anhydride providing good selectivities (β:α > 9:1) in the construction of disaccharides. Importantly, in this case, highly selective glycosylation was observed without the use of 4,6‐ O ‐benzylidene protection, previously considered as crucial for obtaining highly stereoselective coupling reactions 17…”
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