摘要:

Studies aimed at the construction of theC-glycosidic part of nogalamycin (1) and menogarol (2) are described. The stereochemistry of the addition of aryl lithiums to 4-acetyl-1,3-dioxolane16, prepared from D-glucose via10a-15, was studied. The major isomers were the (S)-isomers17aand17bas shown by X-ray analysis of17awith the unnatural configuration. The adduct17awas further converted to the anomeric naphthoquinones22aand22bby acetal cleavage, ozonolysis, acetalization and Diels-Alder reaction with 1-methoxybutadiene.

ISSN:0732-8303    

DOI:10.1080/07328309808002320

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The stereochemistry of the addition of metalloaryls11w-zto the methyl ketones10a-ewas studied in connection with the construction of the hogalamycinC-glycoside. Excellent selectivities towards the (S)-isomer13awere observed in the β-chelate modelBin the reaction of the benzyl ethers10awith the cerium reagent11yand the titanium reagent11zor the alcohol10cwith the lithium compound11w. A moderate 3:1 selectivity in favor of the desired (R)-isomer was observed in the reaction of the silyl ether10dwith11w. A reversal of the addition sequence (reaction of15awith MeMgI) led exclusively to13awhereas the alcohol15cgave a 5:3 mixture of12c:13c.

ISSN:0732-8303    

DOI:10.1080/07328309808002321

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The addition of the metalated 1,4-dimethoxybenzenes17a-cto the methyl ketone14was investigated in connection with the construction of theC-glycosidic part of nogalamycin. In most reactions, a selectivity towards the undesired (S)-isomer16awas observed. However, the reaction of the lithiated aromate17cwith 14 at low temperatures in THF favored the formation of the desired (R)-alcohol15a(15a:16a= 4.8:1) in accordance with the chelate modelA. The selectivity was considerably enhanced in the addition of the more hindered lithiated naphthalene18yielding the (R)-isomer15bexclusively. Reduction of15bafforded the dimethylamino compound19b, a direct precursor of the CDEF-ring system of nogalamycin.

ISSN:0732-8303    

DOI:10.1080/07328309808002322

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A complex between the Forssman pentasaccharide α-D-GalNAc-(1→3)-β-D-GalNAc-(1→3)-α-D-Gal-(1→4)-β-D-Gal-(1→4)-D-Glc and the seed lectin fromDolichos bifloruswas studied using 2D transfer-NOESY (trNOESY) experiments. Experimental transfer-NOE (trNOE) build-up curves of the complex were compared to theoretical values from a complete relaxation and conformational exchange matrix (CORCEMA) calculation. The dissociation constant and the off-rate for the complex formation were determined by fitting experimental intra-glycosidic trNOE build-up curves to corresponding theoretical curves. Atomic coordinates for the complex were taken from a previous homology-modeling study of a complex between the disaccharide fragment α-D-GalNAc-(1→3)-β-D-GalNAc andD. bifloruslectin. The comparison of experimental and theoretical inter-glycosidic trNOEs expands our previous qualitative NMR study and allows further assessment of the quality of the homology modeling study.

ISSN:0732-8303    

DOI:10.1080/07328309808002323

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

In the course of our studies on the synthesis of amphiphilic chitoheptaose derivatives carrying binary long hydrocarbon chains at the reducing sugar, tetradecyl 4-O-(2-amino-2-deoxy-β-D-glucopyranosyl)-2-deoxy-2-tetradecanamido-β-D-glucopyranoside was prepared as a model. For general applicability, the 1,6-anhydro-2-deoxy-2-tetradecanamido-β-D-glucopyranosyl moiety was employed as a precursor of the reducing end. Acetolysis of the 1,6-anhydro ring using triethylsilyl triflate gave an oxazoline intermediate as a major product, accompanied by α-glycosyl acetate as a by-product. Immediate treatment of the mixture with 1-tetradecanol and protic acid followed by a separation work-up efficiently led to tetradecyl β-glycoside derivative.

ISSN:0732-8303    

DOI:10.1080/07328309808002324

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Nickel(II) catalysed isomerisation reactions of C-5 modified derivatives of D-glucose as well as L-idose were investigated. 5-Azido-5-deoxy-D-glucofuranose was successfully isomerised into the corresponding D-mannoepimer in good yields. Contrasting this result, in the case of the 5-modified L-idofuranose probed, no evidence for successful epimerisation at C-2 could be found. However, this sugar was quantitatively rearranged into the corresponding L-sorbopyranose. Upon extended reaction periods, the latter underwent degradation to give the coresponding 4-modified methyl L-xylonate.

ISSN:0732-8303    

DOI:10.1080/07328309808002325

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Methyl 2,3-O-protected α-L-lyxopyranosid-4-uloses (9and19), obtained from L-rhamnose (8), react with 2,5-dimethoxybenzyllithium to afford, with high stereoselectivity, compounds10aand20a, respectively. After protection of the 4-OH group, ethers10band20bwere transformedvia vic-diol deoxygenation reactions into the title compound3and its 4-O-benzyl derivative17. The configuration at C-4 in the alcohol10aand the acetate of its regioisomer12bhas been established by single crystal X-ray analysis.

ISSN:0732-8303    

DOI:10.1080/07328309808002326

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A tetrasaccharide glycoside comprising the core of the sialyl Lewis X structure was synthesized from “building-block” derivatives of the component sugar units. Initially 2-methyl-(3,4,6-tri-O-acetyl-1,2-dideoxy-α-D-glucopyrano)-[2′,1′:4,5]-2-oxazoline (1) was coupled to the known 2-(trimethylsilyl) ethyl 2,3,6,2′,4′,6′-hexa-O-benzyl-β-D-lactoside to give a trisaccharide glycoside (3) in 60% yield. De-O-acetylation, benzylidenation, benzylation, and reductive opening of the benzylidene acetal function of6gave a derivative having OH-4′ open. This derivative was coupled with tetra-O-acetyl-α-D-galactosyl bromide to give a tetrasaccharide in 62% yield, and the product was de-O-acetylated and de-O-benzylated to give the target compound, 2-(trimethylsilyl) ethyl β-D-galactopyranosyl-(1→4)-2-acetamido-2-deoxy-β-D-glucopyranosyl-(1→3)-β-D-galactopyranosyl-(1→4)-β-D-glucopyranoside (11).

ISSN:0732-8303    

DOI:10.1080/07328309808002327

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

13C CP/MAS NMR spectra of powder commercial pectins were recorded and interpreted. NMR spectral results were applied for the calculation of galacturonic acid content (GalA), degrees of methylation (DM) and acetylation (DA). In most cases NMR values from GalA and DM agreed with values obtained by conventional methods (photometry and HPLC). The determination of DA using NMR data was successful only in the case of sugar beet pectin with high acetyl content. The C-6 carbon region was studied in detail and the chemical shift and the shape of peaks in this region were strongly influenced by the ratio of uronic carboxyl forms. Correlation between C-6 carbon chemical shift and DM values for pectins in their protonated form was evaluated.

ISSN:0732-8303    

DOI:10.1080/07328309808002328

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The synthesis of newO-β-D-glucopyranosyl- andO-β-D-galactopyranosyl-2-hydroxyacetaldehyde thiosemicarbazones (5a,b) is reported. Oxidation of allyl glycoside1with KMnO4followed by NaIO4cleavage of the resulting diol2afforded aldehyde3, which was then condensed with thiosemicarbazide and deprotected to give the target compounds (5a,b). Compounds5a,bshowed hydrolytic stability in neutral solution with half-life periods greater than 70 h. The SOD-mimetic activity was determined for the Cu(II) and Mn(II) complexes of5a,b(IC50= 0.2–0.8 mM). This activity is higher by two orders of magnitude than copper (II) bisthiosemicarbazones. The ESR and UV-Vis data of Cu(II)-5asuggest a tetrahedral distortion of the coordination sphere around the central copper atom which could be the reason for their high SOD-mimetic activity.

ISSN:0732-8303    

DOI:10.1080/07328309808002329

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor