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The carbohydrates play a fundamental role in biochemistry. In addition, the purely chemical aspects of these compounds have fascinated the most brilliant chemists through the ages. The organic chemistry of the carbohydrates as multifunctional compounds is very demanding and it is only fairly recently, after years of development of suitable chemical methods, that the full potential of these compounds in synthetic chemistry is being realized (1, 2).
There are different ways to represent the configurations of carbohydrates, but the best-known methods are the Fischer and the Haworth projections. Fischer projections are more suitable for configurational comparisons of carbohydrates, but the Haworth projection is more commonly used today and shows more clearly the cyclic nature of the molecules, which is the overwhelmingly predominant form even in reducing sugars. A stereochemical representation goes a step further in showing the actual structure of these molecules. The fourth method, common with some synthetic chemists, was initially suggested for carbohydrate chemistry by Mills (3). This represents the ring as a flat hexagon in the plane of the paper and the steric arrangement is given as wedged or dashed bonds. The different ways to represent the D-glucose structure are shown in Figure 1.
A recent publication in this Journal presents the isopropylidene group as an introduction to carbohydrate protecting groups (4). This method is one of the earliest methods for protection in carbohydrate chemistry and is still widely used. Because of the multifunctionality of carbohydrates, the development of their use in synthetic chemistry has to a large extent involved protecting group chemistry. The most common protecting methods in carbohydrate chemistry go back to the l9th century (5). The traditional need for protection in carbohydrates was mainly for oligosaccharide synthesis and preparation of rare monosaccharides and related compounds such as L-ascorbic acid (vitamin C). The synthesis of vitamin C by Haworth and Hirst is of historical importance as the first synthesis of a vitamin (6), but Reichstein's and Grussner's synthesis is a dramatic illustration of the industrial potential of a well executed chemical and microbiological synthesis having turned into more than 500 million dollar industry annually (7). Reichstein's synthesis is a brilliant example of the use of the isopropylidene group for protection in carbohydrate chemistry, as well as an early example of...