Hannelore H. Brandstetter

On the side-chain conformation of N-acetylneuraminic acid and its epimers at C-7, C-8, and C-7,8☆

The side-chain conformation of N-acetylneuraminic acid and analogs has been studied by n.m.r. spectroscopy. The results of the 1H-, 13C-n.m.r.-, and 1H-nuclear-Overhauser-enhancement measurements were used to distinguish between different local-minima conformations suggested by hard-sphere calculations. Attempts were made to correlate the major conformation determined for each compound with the behavior towards activation with N-acetylneuraminic acid-CMP-synthetase.

Strukturelle Abwandlungen an N-Acetylneuraminsäuren, 8 Synthese von 7-, 8-, 9-Desoxy- und 4,7-Didesoxyneuraminsäure

The 7- and 8-Iodnonulosonic acid derivatives1 and2 react with tributyltinhydride-AIBN to the 7- and 8-deoxy-N-acetylneuraminic acid derivatives3 a and4 a which after hydrolysis give the 7-deoxy-N-acetylneuraminic acid3 b (5-N-acetamido-3,5,7-trideoxy-β-D-galacto-2-nonulopyranosidonic acid=7-Deoxy-Neu5Ac) and 8-deoxy-N-acetylneuraminic acid4 b (5-N-acetamido-3,5,8-trideoxy-β-D-galacto-2-nonulopyranosidonic acid=8-Deoxy-Neu5Ac). The 4,8,9-tris-(t-butyldimethylsilyl)-N-acetylneuraminic acid derivative5 a yields after transformation to the 7-O-acetyl compound5 b and partial removing of the protecting groups the derivative5 c. Further reaction with theMitsunobu-reagent and methyliodide affords the 9-Iodocompound6 a which turned to the 8-O-acetylderivative6 b. Subsequent reduction by means of tributyltinhydride yields first the 9-deoxyderivative7 a and after hydrolysis the 9-deoxy-N-acetylneuraminic acid7 b (5-N-acetyl amido-3,5,9-trideoxy-D-glycero-β-d-galacto-2-nonulopy-ranosidonic acid=9-Deoxy-Neu5Ac). Another synthesis of7 b follows the route8 f →8 g →7 c. The Deoxy-N-acetylneuraminic acid3 b could be prepared also by an alternative procedure using the methyl-β-8,9-methylethylen-4-O-t-butyldimethylsilyl-N-acetylneuraminic acid methylester8 a via the intermediate compounds8 d and8 e. Application of the 8,9-O-methylethyliden-N-acetylneuraminic acid derivative8 opens an approach to the xanthogenates8 a and8 b which could be reduced to the deoxy-N-acetylneuraminic acid derivatives9 a and10 a. Hydrolysis of10 a yields the 4,7-dideoxy-N-acetylneuraminic acid10 b (5-N-acetamido-3,4,5,7-tetradeoxy-β-D-lyxo-2-nonulopyranosidonic acid=4,7-Dideoxy-Neu5Ac).

Interaction ofN-acetyl-4-, 7-, 8- or 9-deoxyneuraminic acids andN-acetyl-4-, 7- or 8-mono-epi- and-7,8-di-epineuraminic acids withN-acetylneuraminate lyase

Various deoxy- and epi-derivatives ofN-acetylneuraminic acid were synthesized and tested for their substrate properties withN-acetylneuraminate lyase fromClostridium perfringens.N-Acetyl-9-deoxyneuraminic acid is a good substrate,N-acetylneuraminic acid derivatives with epimeric configuration at C-7, C-8 or both are cleaved slowly, whileN-acetyl-4-epi-,N-acetyl-4-deoxy-,N-acetyl-7-deoxy-andN-acetyl-8-deoxyneuraminic acid are resistant to enzyme action.N-Acetyl-4-deoxyneuraminic acid andN-acetyl-4-epineuraminic acid competitively inhibit the enzyme. These studies give further insight into a mechanism proposed for the reversible cleavage of sialic acids byN-acetylneuraminate lyase.

Strukturelle Abwandlungen anN-Acetylneuraminsäure, 3

From methyl-5-acetylamino-7,8-anhydro-4,9-O-bis-(t-butyldimethylsilyl)-3,5-dideoxy-β-D-glycero-D-galacto-2-nonulopyranosidonic acid methylester (1) the derivatives1 a and1 b were obtained by removing the 9-O-(t-butyldimethylsilyl)group withBu4NF, followed by acetylation. Treatment of1 b with 80% acetic acid and acetanhydride/pyridine yields the 8-epi-N-acetylneuraminic acid derivative2 a and the 7-epi-N-acetylneuraminic acid derivative3 a in a ratio of 3:1 (Scheme 1). The structure elucidation of2 b was achieved by converting2 b via the 4,9-bis-O-(tBDMSi)-8-O-tosyl-derivative2 d into the epoxide1 (Scheme 2). Using the same sequence the epoxides4 and5 were transformed into theN-acetylneuraminic acid derivative6 a and the 7,8-bis-epi-N-acetylneuraminic acid derivative7 a (Scheme 3). After treatment with sodium hydroxide and 0.025m HCl and Dowex 50 H+ the 8-epi-, 7-epi- and 7,8-bis-epi-N-acetylneuraminic acids2,3, and7 were obtained. These three compounds were tested withCMP-N-acetylneuraminic acid synthetase.

Strukturelle Abwandlungen an partiell silylierten Kohlenhydraten mittels Triphenylphosphan/Azodicarbonsäurediethylester, 4. Mitt.: Transformationen an Mannose und Galaktose

Reaction of methyl β-D-galactopyranoside (1) with two equivalents oft-butyldimethylchlorosilane yields methyl 2,6-bis-O-(tBDMSi)-β-D-galactopyranoside (1 b), methyl 3,6-bis-O-(tBDMSi)-β-D-galactopyranoside (1 c) and methyl 4,6-bis-O-(tBDMSi)-β-D-galactopyranoside (1 d). Likewise methyl α-D-mannopyranoside (6) affords methyl 2,6-bis-O-(tBDMSi)-α-D-mannopyranoside (6 d) and methyl 3,6-bis-O-(tBDMSi)-α-D-mannopyranoside (6 b), which can be isomerised withTPP/DEAD to methyl 4,6-bis-O-(tBDMSi)-α-D-mannopyranoside (6 f). Methyl 6-O-(tBDMSi)-β-D-galactopyranoside (1 a) and methyl 6-O-(tBDMSi)-α-D-mannopyranoside (6 a) can be prepared from1 or6 with one equivalent oft-butyldimethylchlorosilane.Without an external nucleophile the sugar derivatives1 a and1 b react withTPP/DEAD to form the 3,4-carbonato-β-D-galactopyranosides1 h and1 i and the 3,4-carbonato-2-O-ethoxycarbonyl-β-D-galactoside (1 j). In contrast to the formation of the compound1 i by means ofTPP/DEAD the reaction of1 a withTPP and Di-t-butyl-azodicarboxylate (DTBAD) yields the 2,3-anhydro-β-D-taloside (4 b) and only a small amount of1 i. The epoxide4 b can be cleaved withp-nitrobenzoylchloride/pyridine to the 3-chloro-3-deoxy-2,6-di-O-p-nitrobenzoyl-β-D-idoside (5). Reaction of1 c and1 d withTPP/DEAD yields the 2,3-anhydro-β-D-gulopyranoside (2), which can be transformed with NaN3/NH4Cl to the 2-azido-2-deoxy-β-D-idopyranoside (3).Likewise6 a and6 d can be converted to the 3,4-anhydro-α-D-talosides (7 a and7 b). Reaction of7 b or6 d withTPP/DEAD/NH3 leads to 3,4-anhydro-2-azido-2-deoxy-α-D-galactopyranoside (8) and 3-azido-3-deoxy-α-D-altropyranoside (10), resp.The epoxide7 b is opened with NaN3/NH4Cl to the 4-azido-4-deoxymannosides (11 a and11 c) and the 3-azido-3-deoxy-α-D-idopyranoside (12), while the epoxide8 affords the 2,4-di-azido-2,4-dideoxy-α-D-glucopyranoside (9).Structures were elucidated by1H-NMR-analysis of the corresponding acetates.

Zur Synthese von Sialylglykosiden (Darstellung von Methyl-6-O-benzyl-(4,7,8,9-tetra-O-acetyl-5-acetylamino-3,5-didesoxy-D-glycero-α bzw. β-D-galacto-2-nonulopyranosäure-methylester)-α bzw. β-D-glucopyranosid)

Silver triflate promoted condensations of 5-acetamido-4,7,8,9-tetra-O-acetyl-2-chloro-2,3,5-trideoxy-β-D-glycero-D-galacto-2-nonulopyranosidonic acid methylester with methyl-2,3,4-tri-O-benzyl-α or β-D-glucopyranoside to the title products are reported.

Röntgenstrukturanalyse des Methyl-5-acetylamino-7,8-anhydro-4,9-bis-O-(t-butyldimethylsilyl)-3,5-didesoxy-L-glycero-β-D-galakto-2-nonulopyranosidon-säuremethylesters

An X-ray crystal structure analysis of the title compound was carried out at −168°C in order to assign the stereochemistry around the oxirane: C25H49NO8Si2, trigonal, R3,a=25.18(1),c=13.55(1) Å (hexagonal axes),Z=9,dx=1.105.The structure was solved with direct methods and refined to anR-factor of 0.086.