Title (deu)
Azidonitratisierung und anomerer Effekt
Author
Peter Christoph Burdis
Advisor
Helmut Viernstein
Assessor
Helmut Viernstein
Abstract (deu)
Die Azidonitratisierung von per-O-Acetylcellobial (1) führt zur Bildung von vier Produktfraktionen:
Fraktion I besteht aus dem 2-azido-2-desoxy-β-D-gluco-1-O-nitro Derivat (2) und seinem 2-azido-2-desoxy-α-D-manno-1-O-nitro (3) Isomer. Fraktion II aus dem reinen 2-azido-2-desoxy-α-D-gluco-1-O-nitro-Derivat (4). Die Fraktionen III und IV beinhalten die 2-azido-1,2-didesoxy-α und β-D-gluco-1-acetamido Derivate (7) (8). Durch Umsetzung von Fraktion I mit Tetrabutylammoniumnitrat kann der Großteil von (2) in sein α-Anomer (4) übergeführt werden, während (3) von dieser Reaktion unverändert bleibt. Dies führte zur Entwicklung einer Methode zur Trennung von (2) und (3) über den Umweg der Abreicherung von (2) durch seine Umsetzung in (4) welches eine deutlich andere Retentionszeit gegenüber (2) besitzt. Im Fall der Behandlung von Fraktion II (4) mit Tetrabutylammoniumnitrat werden nur etwa 10% zum 2-azido-2-desoxy-β-D-gluco-1-O-nitro Derivat (2) umgewandelt, während die restlichen 90% von (4) unverändert bleiben. Weiters zeigte sich, dass bei der Umsetzung von Fraktion I mit Eisessig und Natriumacetat hauptsächlich das α-D-glucoacetat (9) und das α-D-mannoacetat (10) entstehen.
Wird analog dazu das 2-azido-desoxy-α-D-gluco-1-O-nitro Derivat (4) aus Fraktion II in gleicher Weise mit Eisessig und Natriumacetat behandelt, entstehen ca. 30% der
α-und β-Acetate (9) und (11), während etwa 40% von (4) unverändert bleiben. Der festgestellte Unterschied in der Reaktivität des β-Nitrats (2) und die relativ hohe Stabilität der α-Nitrate (3) und (4) gegenüber Tetrabutylammoniumnitrat bestätigt das Auftreten des Anomeren Effekts unter diesen Reaktionsbedingungen, welcher dazu führt, dass das axiale Anomer eines Paares von Glycosyl Derivaten mit elektronegativen Substituenten stabiler als das äquatoriale Anomer ist.
Abstract (eng)
Azidonitration and the anomeric effect
The case of per-O-acetyl-cellobial [2,3,4,6- tetra-O-acetyl-β-D-glucopyranosyl(1-4)-3,6-di-O-acetyl-1,5-anhydro-1,2-eno-D-glucitol]
Azidonitration of per-O-acetylcellobial (1) under the conditions described by Lemieux and Ratcliffe (1976) affords essentially four chromatographically separable fractions of products.
Fraction I (app. 32%) is composed of the 2-azido-desoxy- β-D-gluco-1-O-nitro derivate (2) and the 2-azido-desoxy-α-D-manno-1-O-nitro isomer (3) in ratios varying from 15-20 : 1. Fraction II (app. 59%) is the pure 2-azido-desoxy-α-D-gluco-1-O-nitro derivative. (4 ).
Fractions III and IV are the 2-azido-1,2-didesoxy-α and β-D-gluco-1-acetamido derivatives (7) and (8) (ca. 9%). Components (2) and (3) of Fraction I are inseparable by ordinary flash chromatography. Treatment of Fraction I with tetrabutylammonium nitrate converts the mayor portions of (2) into its α-anomer (4) whereas the α-D-manno derivative (3) remains largely unchanged. By contrast, treatment of Fraction II (4) with tetrabutylammonium nitrate affords only app. 10% of the pure β-D-gluco-azido-1-O-nitro derivate (2) while app. 90% of (4) remain unchanged. Treatment of Fraction I with sodium acetate in acetic acid affords mainly the α-D-gluco acetate (9) and the α-D-manno-acetate (10). By contrast, analogous treatment of the α-D-gluco nitrate (4) gives app. 30% of the α-and β-acetates (9) and (11) while app. 40% of (4) remains unchanged.
The observed differences between the reactivity of β-nitrate (2) and the relative stability of the α-nitrates (3) and (4) towards tetrabutylammonium nitrate confirm the operation, in these systems, of the anomeric effect, which causes the axial anomer of a pair of glycosyl derivates with electronegative substituents to be more stable than the equatorial anomer. Considering the anomeric effect, the rather modest yields of 2-azido-1,2-didesoxycellobiose obtainable by azidonitration of per-O-acetylcellobial are explained by the following theory.
The initially formed products of the azidonitration reaction are thus contained in Fraction I, namely the 1,2-trans-products (2) and (3). While the α-D-manno-product (3) is stable under the reaction conditions, the (equatorially disposed) β-D-gluco derivative isomer is thermodynamically unstable and reacts with the nitrate and ammonium ions formed by the reductive decomposition of the cerium (IV)-ammonium hexanitrate complex to form the α-D-gluconitrate (4) and the α-glycosylamine (5). Compound (5) will react with any of the acetate-protected compounds present in the system to form acetamide (7) and partially de-protected polar derivates which presumably escape chromatographic isolation and contribute to the over-all loss of yield. Compound (4) is also subject to reaction with ammonia to form the β-glycosylamine (6) and the acetamido derivate (8). Presently, experiments are under way to trap the unstable intermediate 2 in stable form during the azidonitration reaction, so as to avoid the formation of (4), (7) and (8) and increase the yield of 2-azido-2-desoxy-cellobiose.
Keywords (deu)
AzidonitratisierungLemieuxCellobial
Subject (deu)
Subject (deu)
Type (deu)
Persistent identifier
https://phaidra.univie.ac.at/o:1314411
rdau:P60550 (deu)
52 S. : Ill.
Number of pages
52
Association (deu)
Title (deu)
Azidonitratisierung und anomerer Effekt
Author
Peter Christoph Burdis
Abstract (deu)
Die Azidonitratisierung von per-O-Acetylcellobial (1) führt zur Bildung von vier Produktfraktionen:
Fraktion I besteht aus dem 2-azido-2-desoxy-β-D-gluco-1-O-nitro Derivat (2) und seinem 2-azido-2-desoxy-α-D-manno-1-O-nitro (3) Isomer. Fraktion II aus dem reinen 2-azido-2-desoxy-α-D-gluco-1-O-nitro-Derivat (4). Die Fraktionen III und IV beinhalten die 2-azido-1,2-didesoxy-α und β-D-gluco-1-acetamido Derivate (7) (8). Durch Umsetzung von Fraktion I mit Tetrabutylammoniumnitrat kann der Großteil von (2) in sein α-Anomer (4) übergeführt werden, während (3) von dieser Reaktion unverändert bleibt. Dies führte zur Entwicklung einer Methode zur Trennung von (2) und (3) über den Umweg der Abreicherung von (2) durch seine Umsetzung in (4) welches eine deutlich andere Retentionszeit gegenüber (2) besitzt. Im Fall der Behandlung von Fraktion II (4) mit Tetrabutylammoniumnitrat werden nur etwa 10% zum 2-azido-2-desoxy-β-D-gluco-1-O-nitro Derivat (2) umgewandelt, während die restlichen 90% von (4) unverändert bleiben. Weiters zeigte sich, dass bei der Umsetzung von Fraktion I mit Eisessig und Natriumacetat hauptsächlich das α-D-glucoacetat (9) und das α-D-mannoacetat (10) entstehen.
Wird analog dazu das 2-azido-desoxy-α-D-gluco-1-O-nitro Derivat (4) aus Fraktion II in gleicher Weise mit Eisessig und Natriumacetat behandelt, entstehen ca. 30% der
α-und β-Acetate (9) und (11), während etwa 40% von (4) unverändert bleiben. Der festgestellte Unterschied in der Reaktivität des β-Nitrats (2) und die relativ hohe Stabilität der α-Nitrate (3) und (4) gegenüber Tetrabutylammoniumnitrat bestätigt das Auftreten des Anomeren Effekts unter diesen Reaktionsbedingungen, welcher dazu führt, dass das axiale Anomer eines Paares von Glycosyl Derivaten mit elektronegativen Substituenten stabiler als das äquatoriale Anomer ist.
Abstract (eng)
Azidonitration and the anomeric effect
The case of per-O-acetyl-cellobial [2,3,4,6- tetra-O-acetyl-β-D-glucopyranosyl(1-4)-3,6-di-O-acetyl-1,5-anhydro-1,2-eno-D-glucitol]
Azidonitration of per-O-acetylcellobial (1) under the conditions described by Lemieux and Ratcliffe (1976) affords essentially four chromatographically separable fractions of products.
Fraction I (app. 32%) is composed of the 2-azido-desoxy- β-D-gluco-1-O-nitro derivate (2) and the 2-azido-desoxy-α-D-manno-1-O-nitro isomer (3) in ratios varying from 15-20 : 1. Fraction II (app. 59%) is the pure 2-azido-desoxy-α-D-gluco-1-O-nitro derivative. (4 ).
Fractions III and IV are the 2-azido-1,2-didesoxy-α and β-D-gluco-1-acetamido derivatives (7) and (8) (ca. 9%). Components (2) and (3) of Fraction I are inseparable by ordinary flash chromatography. Treatment of Fraction I with tetrabutylammonium nitrate converts the mayor portions of (2) into its α-anomer (4) whereas the α-D-manno derivative (3) remains largely unchanged. By contrast, treatment of Fraction II (4) with tetrabutylammonium nitrate affords only app. 10% of the pure β-D-gluco-azido-1-O-nitro derivate (2) while app. 90% of (4) remain unchanged. Treatment of Fraction I with sodium acetate in acetic acid affords mainly the α-D-gluco acetate (9) and the α-D-manno-acetate (10). By contrast, analogous treatment of the α-D-gluco nitrate (4) gives app. 30% of the α-and β-acetates (9) and (11) while app. 40% of (4) remains unchanged.
The observed differences between the reactivity of β-nitrate (2) and the relative stability of the α-nitrates (3) and (4) towards tetrabutylammonium nitrate confirm the operation, in these systems, of the anomeric effect, which causes the axial anomer of a pair of glycosyl derivates with electronegative substituents to be more stable than the equatorial anomer. Considering the anomeric effect, the rather modest yields of 2-azido-1,2-didesoxycellobiose obtainable by azidonitration of per-O-acetylcellobial are explained by the following theory.
The initially formed products of the azidonitration reaction are thus contained in Fraction I, namely the 1,2-trans-products (2) and (3). While the α-D-manno-product (3) is stable under the reaction conditions, the (equatorially disposed) β-D-gluco derivative isomer is thermodynamically unstable and reacts with the nitrate and ammonium ions formed by the reductive decomposition of the cerium (IV)-ammonium hexanitrate complex to form the α-D-gluconitrate (4) and the α-glycosylamine (5). Compound (5) will react with any of the acetate-protected compounds present in the system to form acetamide (7) and partially de-protected polar derivates which presumably escape chromatographic isolation and contribute to the over-all loss of yield. Compound (4) is also subject to reaction with ammonia to form the β-glycosylamine (6) and the acetamido derivate (8). Presently, experiments are under way to trap the unstable intermediate 2 in stable form during the azidonitration reaction, so as to avoid the formation of (4), (7) and (8) and increase the yield of 2-azido-2-desoxy-cellobiose.
Keywords (deu)
AzidonitratisierungLemieuxCellobial
Subject (deu)
Subject (deu)
Type (deu)
Persistent identifier
https://phaidra.univie.ac.at/o:1314412
Number of pages
52
Association (deu)
License
Citable links
Other links
Managed by
Details
Metadata
Export formats
Universitätsring 1, 1010 Wien | T
T +43-1-4277-0