Haworth Memorial Lecture. The sweeter side of chemistry

Abstract

Sir Walter Norman Haworth's researches played an important role in the determination of the molecular structure of sucrose and he was fully aware of its potential 'as a source of new industrial materials and intermediates'. After World War 2, he organized a research programme at the University of Birmingham on 'The Utilisation of Sucrose',2 under Dr. Leslie F. Wiggins and supported by the Colonial Products Research Council, with a view to finding a market for surplus sugar. Their efforts were concentrated upon degradation products, such as furfural and its derivatives, and it is noteworthy that the review written by Wiggins in 1947 cites only a few genuine sucrose derivatives, mostly octa-substituted, owing to the difficult experimental problems in handling sucrose. Studies were hampered by the multiplicity of hydroxy-groups on sucrose and its sensitivity to acid, coupled with its limited solubility in organic solvents and the lack of suitable protective groups, since standard procedures usually failed. The energy crisis of the 1970s focussed attention on the economic potential of sucrose as an ubiquitous feed stock for chemical and microbiological exploitation, consequently chemical studies have taken on an added importance.Sucrose (1) is a non-reducing disaccharide with eight hydroxy-groups, arranged in the crystal with a conformation3 in which the a-D-glUCOpyranOSyl unit is 4C, whilst the P-D-fructofuranoside unit is 3T4 (2), and the two units are bridged by two intramolecular hydrogen bonds (3) from 0-6' to 0 -5 and 0 -1 to 0-2. The unprimed and primed numbers are used to indicate the carbons, and associated oxygen atoms, in the glucosyl and fructoside units respectively. In solution the overall conformation is similar to that found in the crystal, particularly around the inter-glycosidic linkage (3), as revealed by 'Hand I3C-n.m.r. ~p e c t r a . ~ The original chemical synthesis of natural D-sucrose (1) by Lemieux and Huber in 1953 was preceded by its enzymic synthesis in 1944,6 and followed in 1978 by a synthesis ' of * Delivered at the Spring Meeting ofthe Royal Society ofchemistry Carbohydrate Group on 1st April 1985 at the University of Bristol.

Evolution of the Structural Representation of Sucrose [1]

“…The first measurements accurate enough to locate the positions of the hydrogen atoms, were based on neutron diffraction data by Brown and Levy in 1963 [23], which upon later refinement [24,25] resulted in structure 15: the glucose portion adopts a 4C1 conformation whereas that of the fructofuranose residue is a 4T3 twist. The two rings are approximately at right angles, yet the overall structure, most notably, is determined by two strong intramolecular hydrogen bonds: one between the terminal 6'-OH of fructose to the pyranoid ring oxygen of 1.89 A length, the other, even shorter, reaching fr9m the primary 1'-OH of fructose to 0-2 of glucose (1.85 A), as depicted in formulae 16 [24], 17 [26], and 18 [27]. These hydrogen bonds serve to fix the molecule in a well-ordered, rigid conformation.…”