Carbohydrates Haworth forms

All of this work was set aside in 1932, when Haworth formed most of the carbohydrate workers into a team (or syndicate ) to investigate the structure of Szent-Gyorgyi s hexuronic acid, which proved to be vita-... 

Structural drawings of carbohydrates of this type are called Haworth formulas, after the British chemist Sir Walter Norman Haworth (St Andrew s University and the University of Birmingham) Early m his career Haworth contributed to the discovery that carbohydrates exist as cyclic hemiacetals rather than m open chain forms Later he col laborated on an efficient synthesis of vitamin C from carbohydrate precursors This was the first chemical synthesis of a vitamin and provided an inexpensive route to its prepa ration on a commercial scale Haworth was a corecipient of the Nobel Prize for chem istry m 1937... 

Haworth formulas are satisfactory for representing configurational relationships in pyranose forms but are uninformative as to carbohydrate conformations X ray crystal lographic studies of a large number of carbohydrates reveal that the six membered pyra nose ring of D glucose adopts a chair conformation... 

Haworth formulas (Section 25 6) Planar representations of furanose and pyranose forms of carbohydrates... 

The manner in which sugars are linked together to form oligosaccharides was elucidated by W. N. Haworth, who received the Nobel Prize in chemistry in 1937 for this and other contributions to research on the structures and reactions of carbohydrates. 

The first observation of the instability of carbohydrate orthoesters toward alkali came from Haworth, Hirst and Miller in connection with their experiments on the simultaneous deacetylation and methylation of L-rhamnose methyl 1,2-orthoacetate. These authors noticed that methylation by methyl iodide and silver oxide in the presence of solid sodium hydroxide resulted in the formation of crystalline methyl tri-methyl-/3-L-rhamnopyranoside. A similar result was obtained by Bott, Haworth and Hirst on the simultaneous deacetylation and methylation of triacetyl-D-mannose methyl 1,2-orthoacetate by the use of excessive quantities of dimethyl sulfate and alkali. The reaction produced a mixture of a. and /3 forms of methyl tetramethyl-D-mannopyranoside but the yield was only 40%. When the acetylated orthoester was submitted to methylation with silver oxide and methyl iodide in the presence of sodium hydroxide, the product was mainly trimethyl-rhamnose methyl 1,2-orthoacetate. This result indicates that for the alkaline hydrolysis of orthoesters, hydroxyl ions are necessary. Such ions are present in the dimethyl sulfate-alkali process, but are absent in the methyl iodide treatment except when the reaction mixture contains a little water either by accident or from the decomposition of the sugar molecule. Haworth, Hirst and Samuels examined the behavior of dimethyl-L-rhamnose methyl 1,2-orthoacetate in alkaline solution. When the substance was heated under various conditions with 0.1 A alkali at 70 there was no appreciable hydrolysis at the end of ninety minutes, whereas at 80 for... 

PROBLEM 25.5 Write Haworth formulas corresponding to the furanose forms of each of the following carbohydrates ... 

Many carbohydrates exist in equilibrium between open chain and 5- or 6-membered cyclic forms. The cyclic pyranoses (5-ring) or hexanoses (6-ring) are produced from an intramolecular cyclisation of an alcohol group onto an aldehyde, leading to the formation of a hemiacetal (see Section 8.3.5). These are most commonly drawn as Haworth projections, in which the ring is drawn as a hexagon and vertical lines attach substituents. 

Haworth formulas are satisfactory for representing configurational relationships in pyranose forms but are uninformative as to carbohydrate conformations. X-ray... 

Figure 2.27) ° In these drawings the cyclic hemiacetal form of the carbohydrate is shown as a six-membered ring in the chair conformation. An older representation of carbohydrates that represents structures with planar six-membered rings is the Haworth drawing 64b. ... 

Haworth formulas are named after the English chemist W. N. Haworth (University of Birmingham), who, in 1926, along with E. L. Hirst, demonstrated that the cyclic form of glucose acetals consists of a six-membered ring. Haworth received the Nobel Prize for his work in carbohydrate chemistry in 1937. For an excellent discussion of Haworth formulas and their relation to open-chain forms, see The Conversion of Open Chain Structures of Monosaccharides into the Corresponding Haworth Formulas, Wheeler, D. M. S., Wheeler, M. M., and Wheeler, T. S.,J. Chem. Educ. 1982, 59, 969-970. 

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