Introduction

Although the two parts of this report are now being published separately , the general format and coverage of this section, covering the organic chemistry of mono-, di-, and tri-saccharides, has not been changed. It might be helpful to point out firstly that a hard and fast division has not been drawn between trisaccharides and higher oligosaccharides, particularly in the chapters dealing with glycosides and antibiotics, and secondly that the coverage on glycosides, antibiotics, nucleosides and related compounds containing carbohydrate units is selective for those papers where there is judged to be some specific carbohydrate interest besides any for the aglycone components; in the fringe areas, we hope this principle is acceptable in the interests of keeping the report within reasonable, economic limits.

The trends in research endeavour noted in recent reports have been continued, and the extensive sections on glycoside synthesis, antibiotics and nucleosides reflect the major interest in these areas. The synthesis of tri- and higher oligosaccharides is fast becoming a routine procedure for providing substrates of immunochemical interest. New antibiotic materials continue to be discovered consisting mainly or entirely of carbohydrate components in complex structures, and a ever widening variety of nucleoside analogues have been reported. These areas pose problems in classification, and we hope the distinctions that have been drawn between nucleosides on the one hand and miscellaneous nitrogen compounds on the other have not been too arbitrary for general acceptance. Another growth area has been the application of carbohydrates as chiral templates for the synthesis of a wide range of naturally occurring chiral compounds. Chapters 20 and 21 reflect the fruitful application of both routine and newer developments in spectroscopic techniques for the analysis of carbohydrate compounds and illustrate how much can be learned about relatively complex materials without actually doing any chemistry on them.

Recommendations for the nomenclature of unsaturated and branched-chain sugars, and of conformations of five and six-membered rings have been published during the year.

Free Sugars

The main pathways of reaction of primary free radicals in carbohydrates have been reviewed. A review on the use of sugars in fermentation and for preparation of sweeteners, plastics and chemicals has appeared.

The tastes of chlorinated derivatives of simple monosaccharides have been compared with those of the parent sugars and the di-saccharides maltose and trehalose in relation to existing theories of the sweetness sensation.

Isolation and Synthesis

The isolation by gel chromatography of D-threo-pent-2-ulose from the lipopolysaccharide of Pseudomonas diminuta NCTC 8545 represents the first time this sugar has been observed in a microbial polymer.

Two reviews of the formose reaction by the same authors have appeared, and in two further papers an overall model for the reaction catalysed by calcium hydroxide is described. A key observation that sublimed paraformaldehyde was not transformed into sugars led to the suggestion that carbohydrates may be naturally present in p.p.m. quantities in parraformaldehyde and cause autocatalysis. Glycolaldehyde at 3 p.p.m. is sufficient to initiate autocatalysis. In the absence of traces of sugars the Cannizzaro reaction yielding methanol and formate occurred.

A solution of formose is an effective catalyst for converting formaldehyde to monosaccharides when used in 0.25 - 0.50 wt.% quantities. The induction period was shortened to one-sixth, and the Cannizzaro reaction was reduced by half with concomitant increased yield of moonosaccharides from 42 to 60%. Optimization of carbohydrate production in the formose reaction using calcium oxide and formose as co-catalysts gave an overall yield of 76.5%, comprised of hexoses (71%), pentoses (23%) and tetroses (6%). The formose reaction has been studied at cryogenic temperatures: under u.v. irradiation at 20-80K solid formaldehyde underwent polyaddition and polymerization to give polyoxymethylene. A mixture of simple aldoses resulted. A study of the catalytic activity of inorganic bases towards the Cannizzaro reaction of formaldehyde has shown that barium hydroxide is more effective than calcium hydroxide, and both are considerably more active than magnesium hydroxide. Selectivity for the Cannizzaro reaction increased on addition of copper powder, copper sulphate, ferric sulphate, bismuth chloride, or boric acid, was unaffected by addition of iron or magnesium powder, and decreased by added tin (IV) chloride. Decreasing the temperature from 40 to 10°C reduced the induction period, reaction time and yield of Cannizzaro products but increased the yield of sugar derivatives. Zinc oxide has been shown to catalyse the formose reaction to give a complex mixture of sugars at pH 5.5 without the; Cannizzaro side reaction. Addition of D-glucose or reduction of the formaldehyde-zinc oxide ratio eliminated the otherwise long induction period. G.c. analysis of the formose products under different reaction conditions with calcium salts as catalysts has shown that the complexity of the product distribution was controlled by the ratio of calcium ion-formaldehyde concentrations. A study of the formose reaction in methanol has been conducted. 15 Amines and free amino-acids can provide a necessary complementary interaction between the asymmetric carrier, the metal catalyst, and the synthesized enantiomeric forms of sugars in the formose reaction. Thus heptulose, D-manno-oxoheptulose, and D-fructose were obtained in a process utilizing a cellulose carrier and an amino-acid, with calcium and magnesium oxides as catalyst. The product mixture contained 22% neutral and 78% acidic sugars. A study of the catalytic activity of benzoyl carbinol and its 4-methoxy-, 3-chloro-, 4-chloro-, and 2,5-di-chloro-derivatives on the condensation of formaldehyde in the presence of triethylamine and lead or calcium hydroxide has confirmed that electron-donating substituents in the organic co-catalyst decreased its catalytic activity and vice versa. The rate of condensation did not depend on the concentration of formaldehyde. A selective formose reaction occurs giving 3-C-(hydroxy-methyl)-pentofuranose (1) when the major part of the calcium ions are removed as sparingly soluble salts at the end of the induction period,...