System for classification of structurally related carbohydrates

Abstract

A system is presented for the classification of structurally and configurationally related carbohydrates. Each substance is assigned a code number that defines the structure and configuration. By inspection of the code numbers, or by a punched-card technique, groups of structurally related carbohydrate derivatives can be selected readily from a heterogeneous collection. The structures, configurations, and conformations of pyranose and furanose derivatives are discussed, and classifications are made on the basis of a few fundamental structures. Certain ambiguous and objectionable features in the classification of pyranose ring conformations in the CI and 1C categories of Reeves are pointed out. In this paper, CI denotes the chair conformation in both the D and the L aldohexose series in which the reference group attached to carbon 5 of the ring is in the equatorial position. Similarly, C2 denotes the chair conformation in both series in which the reference group attached to carbon 5 of the ring is in the axial position. Xylose and sorbose are classified like glucose; lyxose and tagatose like mannose; arabinose and fructose like galactose; and ribose and psicose like talose. Because the designations are independent of the D or L series, they avoid the erro­ neous classification of enantiomorphs in different conformations. During the past several years the infrared absorp­ tion spectra of a large group of carbohydrate de­ rivatives have been measured at the Bureau with the object of providing reference spectra and data for structurally related materials. A classification system was devised to show the structure and con­ figuration of the compounds by means of numbers suitable for coding and separating by punched-card techniques. Although the system was developed primarily for comparing infrared absorption spectra, it can be used for classifying structurally related carbohydrates for any purpose. The code numbers are assigned by means of a key outlined in tables 1 and 2. A decimal point is in­ serted after the second digit to separate figures that provide broad generic classification from those that show definite structure: For example, a-D-glucopyranose is given the code number 10.2110. Reading from left to right, 1 shows that the sub­ stance is a monosaccharide; 0, that the hydroxy! groups are predominantly unsubstituted; 2, that it has a primary 6-carbon structure; 1, that it has the glucose configuration; 1, that it has a Cl pyranose ring with an axial glycosidic group, and 0 that the glycosidic hydroxy] is not substituted. The code numbers for all a-D-glucopyranose structures will have the .211 sequence. Each structural grouping has a characteristic sequence of numbers. Hence by inspection of the numbers, or by punched-card technique, grpups of structurally and configurationally related carbohydrate derivatives can be readily selected. The classifications are not intended for general nomenclature and no changes are proposed in the rules for naming carbohydrates. In subsei The work reported in this publication was sponsored by the Office of Naval Research as part of a program on the investigation of the structure, configuration, and ring conformation of the sugars and their derivatives by infrared absorption measurements (NRO 55208^. The classification system presented here has been used to classify the infrared spectra of about 200 carbohydrate derivatives. The spectra and reference numbers will appear in forthcoming publications. quent paragraphs the structural elements involved in classification will be considered in order, and directions will be given for assigning code numbers. 2. Components of the Code Number