Glycal is a name for cyclic enol ether derivatives of sugars having a double bond between carbonatoms 1 and 2 of the ring. The term "glycal" should not be used for an unsaturated sugar that has a double bond in any position other than between carbon atoms 1 and 2.[1]
The first glycal was synthesized by Hermann Emil Fischer and Karl Zach in 1913.[2] They synthesized this 1,2-unsaturated sugar from D-glucose and named their product D-glucal. Fischer believed he had synthesized an aldehyde, and therefore he gave the product a name that suggested this.[3] By the time he discovered his mistake, the name "glycal" was adopted as a general name for all sugars with a double bond between carbon atoms 1 and 2.[4]
Conformationedit
Glucal in its preferred half-chair conformation
Glycals can be formed as pyranose (six-membered) or furanose (five-membered) rings, depending on the monosaccharide used as a starting material to synthesize the glycal. Glycals can also be classified as endo-glycals or exo-glycals. A glycal is an endo-glycal when the double bond is within the ring. If the hydroxyl group on carbon 1 has been replaced with another carbon atom, a double bond can also form outside the ring between carbon 1 and this new carbon. In this case, the product is called an exo-glycal.[5] The glycal conformation that has been studied in most depth is that of the pyranose endo-glycal. The favoured conformation of this glycal is the half-chair,[6] a result which has been confirmed by quantum mechanical calculations.[7]
Synthesisedit
The original Fischer glycal synthesis was the reductive elimination with zinc of a glycosyl halide. This glycosyl halide was formed from a monosaccharide starting material.[8] Some other synthetic routes include:
Reaction of thioglycosides with lithium napthalenide.[10]
Mesylation of the anomeric hydroxyl and formation of the anomeric palladium complex, which undergoes beta-elimination[10]
A general example of each synthetic route is given below (drawn with first discussed synthesis bottom right, moving clockwise):
Some available methods to synthesize glycals
Reactions and usesedit
The double bond of a glycal allows many other functional groups to be introduced into a monosaccharide. Like an alkene, a glycal can undergo electrophilic addition across the double bond to add in these new atoms such as halogens, epoxides, and nitrogen. The glycal double bond also allows a deoxy position (carbon in the ring that doesn’t have an oxygen bonded to it) to be easily introduced.[8]
Glycals have many uses in synthetic carbohydrate chemistry. They are commonly used as glycosylation donors, meaning that they can react with other monosaccharides to form a longer chain of monosaccharides called an oligosaccharide.[11]
Glycals can also have interesting applications in studying biological systems, particularly enzymes. D-glucal and radiolabelled D-galactal have been used to selectively bind with amino acids in the active sites of several enzymes. These enzyme-glycal complexes allow these amino acids that are essential for catalysis to be identified and allow for a better understanding of how these enzymes function.[12]
^Ernst, C.; Piacenza, M.; Grimme, S.; Klaffke, W. (2003). "Epoxidation of C-branched glycals: unexpected stereochemical results and their theoretical rationale". Carbohydrate Research. 338 (3): 231–236. doi:10.1016/S0008-6215(02)00406-8. PMID 12543555.
^ abLindberg, T.J.; Harmata, M.; Wender, P.A. (2004). Strategies and Tactics in Organic Synthesis. Academic Press. ISBN0-12-450287-3.
^Calimente, D.; Postema, M.H.D. (1999). "Preparation of C-1 Glycals via Olefin Metathesis. A Convergent and Flexible Approach to C-Glycoside Synthesis". The Journal of Organic Chemistry. 64 (6): 1770–1771. doi:10.1021/jo982331o. PMID 11674258.
^ abSomsk, L. (2001). "Carbanionic Reactivity of the Anomeric Center in Carbohydrates". Chemical Reviews. 101 (1): 81–136. doi:10.1021/cr980007n. PMID 11712195.
^Danishefsky, S.J.; McClure, K.F.; Randolf, J.T.; Ruggeri, R.B. (1993). "A Strategy for the Solid-Phase Synthesis of Oligosaccharides". Science. 260 (5112): 1307–1309. Bibcode:1993Sci...260.1307D. doi:10.1126/science.8493573. PMID 8493573.
^Sigman, D.S. (1992). Mechanisms of Catalysis. Academic Press. ISBN0-12-122720-0.
glycal, name, cyclic, enol, ether, derivatives, sugars, having, double, bond, between, carbon, atoms, ring, term, glycal, should, used, unsaturated, sugar, that, double, bond, position, other, than, between, carbon, atoms, glucal, glycal, formed, from, glucose. Glycal is a name for cyclic enol ether derivatives of sugars having a double bond between carbon atoms 1 and 2 of the ring The term glycal should not be used for an unsaturated sugar that has a double bond in any position other than between carbon atoms 1 and 2 1 Glucal the glycal formed from glucose Contents 1 History 2 Conformation 3 Synthesis 4 Reactions and uses 5 References 5 1 See alsoHistory editThe first glycal was synthesized by Hermann Emil Fischer and Karl Zach in 1913 2 They synthesized this 1 2 unsaturated sugar from D glucose and named their product D glucal Fischer believed he had synthesized an aldehyde and therefore he gave the product a name that suggested this 3 By the time he discovered his mistake the name glycal was adopted as a general name for all sugars with a double bond between carbon atoms 1 and 2 4 Conformation edit nbsp Glucal in its preferred half chair conformation Glycals can be formed as pyranose six membered or furanose five membered rings depending on the monosaccharide used as a starting material to synthesize the glycal Glycals can also be classified as endo glycals or exo glycals A glycal is an endo glycal when the double bond is within the ring If the hydroxyl group on carbon 1 has been replaced with another carbon atom a double bond can also form outside the ring between carbon 1 and this new carbon In this case the product is called an exo glycal 5 The glycal conformation that has been studied in most depth is that of the pyranose endo glycal The favoured conformation of this glycal is the half chair 6 a result which has been confirmed by quantum mechanical calculations 7 Synthesis editThe original Fischer glycal synthesis was the reductive elimination with zinc of a glycosyl halide This glycosyl halide was formed from a monosaccharide starting material 8 Some other synthetic routes include Ring closing metathesis 9 Reaction of thioglycosides with lithium napthalenide 10 Mesylation of the anomeric hydroxyl and formation of the anomeric palladium complex which undergoes beta elimination 10 A general example of each synthetic route is given below drawn with first discussed synthesis bottom right moving clockwise nbsp Some available methods to synthesize glycalsReactions and uses editThe double bond of a glycal allows many other functional groups to be introduced into a monosaccharide Like an alkene a glycal can undergo electrophilic addition across the double bond to add in these new atoms such as halogens epoxides and nitrogen The glycal double bond also allows a deoxy position carbon in the ring that doesn t have an oxygen bonded to it to be easily introduced 8 Glycals have many uses in synthetic carbohydrate chemistry They are commonly used as glycosylation donors meaning that they can react with other monosaccharides to form a longer chain of monosaccharides called an oligosaccharide 11 Glycals can also have interesting applications in studying biological systems particularly enzymes D glucal and radiolabelled D galactal have been used to selectively bind with amino acids in the active sites of several enzymes These enzyme glycal complexes allow these amino acids that are essential for catalysis to be identified and allow for a better understanding of how these enzymes function 12 References edit IUPAC Nomenclature of Carbohydrates GLYCALS Extensive interesting and inexpensive starting materials for building blocks synthesis Archived from the original on 2009 06 05 Retrieved 2018 11 30 Lindhorst T K 2007 Essentials of Carbohydrate Chemistry and Biology Wiley VCH ISBN 978 3 527 31528 4 Fraser Reid B O Tatsuta K Thiem Joachim 2001 Glycoscience Chemistry and Chemical Biology I III Springer ISBN 3 540 67764 X Taillefumier C Chapleur Y 2004 Synthesis and Uses of exo Glycals Chemical Reviews 104 1 263 292 doi 10 1021 cr030640v PMID 14719977 Pigman W W Wolfrom M L Tipson R S 1950 Advances in Carbohydrate Chemistry Academic Press ISBN 0 12 007226 2 Ernst C Piacenza M Grimme S Klaffke W 2003 Epoxidation of C branched glycals unexpected stereochemical results and their theoretical rationale Carbohydrate Research 338 3 231 236 doi 10 1016 S0008 6215 02 00406 8 PMID 12543555 a b Lindberg T J Harmata M Wender P A 2004 Strategies and Tactics in Organic Synthesis Academic Press ISBN 0 12 450287 3 Calimente D Postema M H D 1999 Preparation of C 1 Glycals via Olefin Metathesis A Convergent and Flexible Approach to C Glycoside Synthesis The Journal of Organic Chemistry 64 6 1770 1771 doi 10 1021 jo982331o PMID 11674258 a b Somsk L 2001 Carbanionic Reactivity of the Anomeric Center in Carbohydrates Chemical Reviews 101 1 81 136 doi 10 1021 cr980007n PMID 11712195 Danishefsky S J McClure K F Randolf J T Ruggeri R B 1993 A Strategy for the Solid Phase Synthesis of Oligosaccharides Science 260 5112 1307 1309 Bibcode 1993Sci 260 1307D doi 10 1126 science 8493573 PMID 8493573 Sigman D S 1992 Mechanisms of Catalysis Academic Press ISBN 0 12 122720 0 See also edit Ferrier rearrangement Chemical glycosylation Retrieved from https en wikipedia org w index php title Glycal amp oldid 1165240184, wikipedia, wiki, book, books, library,
