Journal of Research of the National Bureau of Standards Vol. 57, No.3, September 1956 Research Paper 2707 System for Classification of Structurally Related Carbohydrates 1 Horace S. Isbell A system is presented fo r t he classifi cation of structura lly a nd confi gurationally related carbohydrates. Each substance is assigned a code number t hat defines t he s tructure a nd configuration. By inspection of t he code numbers, or by a punched-card technique, groups of structurally related carbohydrate derivatives can be selected read il y from a heterogeneous collection . The structures, configurations, and conformations of pyranose a nd furanose der ivatives are di scussed, and classifications are made on t he basis of a few fundamental structures. Certain ambiguous and objectionable features in the classifi cation of p y ranose ring conformations in t he Cl and I C categori es of Reeves are pointed out. In this pa per, C I denotes t he chair confor mat ion in both the D and the L aldohexose se1'ies in which t he reference group attached to carbon 5 of t he ring is in the equatorial position. Sim ilarly, C2 denotes t he chaiT con formation in bot h seri es in which the reference group attached to carbon 5 of t he ring is in t he axial position. Xylose and sorbose are classifi ed like glucose; lyxose and t agatose lik e mannose; arabinose a nd fructose like galactose; and ribose and psicose like talose. Because the designations al'C indcpendent of t he D or L series, they avoid t he erro­ neo us classifi cation of cnant iomol'phs in diff erent conformations. 1. Introduction quent paragraphs the structural elements involved in classification will be considered in order, and During thc past sevcral ycars the infrared absorp­ directions will be given for assigning code numbers. tion spectra of a large group of carbohydrate de­ rivatives have been m easured at the Bureau with 2 . Components of the Code Number the object of providing reference spectra and data for structurall y related materials. A classification 2.1. Type of Carbohydra te system was devised to show the structure and con­ figuration of the compounds by means of numbers The first digit in the code number divides the suitable for coding and separating by punched-card carbohydrates into groups of increasing complexity: techniques. Although the system was developed 1 signifies a monosaccharide; 2, a disa,ccharide; 3, an primarily for comparing infrared abso rption spectra, oligosaccharide; 4, a polysaccharide composed of one it can be used for classifying structurally related type of unit; and 5, a polysaccharide co mposed of a carbohydrates for any purpose . variety of units. Substances in types 1 to 4 are The code nwnbers arc assigned by means of a key given definitive code numbers but no attempt is outlined in tables 1 and 2. A decimal poillt is in­ made to classify substances in 5, beyond codillg the serted after the second digit to separate fi gures that structural units present. provide broad generic classification from those that show definite structure: For example, a-D-glu­ 2.2. Major Substituent copyranose is given the code number 10.2110. Reading from left to right, 1 shows that the sub­ The second digit is assigned to show substitution stance is a monosaccharide; 0, that the hydroxyl on the polyol structure. When half or more of the groups are predominantly unsubstituted; 2, that it hydroxyls are free, the classification number is 0; has a primary 6-carbon structure; 1, that it has the when more than half of the hydroxyls ar c substituted glucose configuration ; 1, that it has a C1 pyranose the number corresponds to the substituent present in ring with an axial glycosidic group, and 0 that the predominating amount. If two classifications are glycosidic hydroxyl is not substituted. The code possible, the one with the lower number is used. numbers for all a-D-glucopyranose structures will have the .211 sequen ce . Each structural grouping 2.3. Carbon Skeleton has a, characteristic sequence of numbers. Hence The first digit to the right of the decimal point by inspection of the numbers, or by punched-card defines the skeleton of the fundamental carbon chain. technique, groups of structurally and confi guration­ Alcohols, aldoses, aldonic acids, uronic acids, etc., are ally related carbohydrate derivatives can be readily classified as primary; ketoses and related compounds selected. The classifications arc not intended for as secondary. Cyclitols and higher sugars are in­ general nomellclature [md no changes are proposed cluded in a miscellaneous group, 9. The aldo­ in the rules for naming carbohydrates. In su bse- heptoses are placed in t wo groups designated as 7a 1 The work reported in this pllblication was sponsored by tbc Office or Naval and 7b. Substances in the 7a group have like con­ Rewarch as part ora program on the investigation of the structure, configuration, figurations for the two configurational units given in and ring conformation of the sugars and thei,· derivatives by infrared absorption measurements (NRO 552081. The classifi cation system presented here has the conventional ACS name [1]; 2 those in the 7b been used to classify th~ infrared spectra of about 200 carbohydrate derivatives. The spectra and reference numbers will appear in forthcoming publications. 2 Figures in brackets indicate the li terature references at the end of this paper. 171 TABLE 1. Classification key for code nwnbers Code I!. 'J'ypeofcarbohydratc 2. Major substituent 3. Carbon skeleton 4. Configuration 5. Characteristic unit 6. Substituen t ou main functional gro up · o Not substituted < 5 primary R acemic Anomeric mixture Not substituted. 1 Monosaccharide M ethylated 5 primary glueo ","Pyranose Cl 2 nisaccharide Acetylated 6 primary manno e-Pyranose C 1 3 Oligosaccharide Nitrated 7a primary gala!:lo a-Pyranose C2 4 P olysaccharide 7b primary tala e-Pyranose C 2 [See table 2 fo)' list of (s imple) substituents.] Polysaccharide < 5 secondary ida Ot her pyranose (complex) (j t, secondary g1l10 Furanose 7 6 secondary alt ro GIycitol 8 7 secondary allo Aldehydo or keto deri v­ ative. Misce ll a n~ o us M iscellaneous Miscellaneous Miscellaneous Acid derivative • Asterisk is used to indicate linkage in higher saccharides. TABLE 2. Numbers for substituent groups and auxiliary stncetlues Code Substituent group Code Substituent gro up Code Substituent group Code A uxiliary structure --- I 0 None. 10 OH grou p. 30 Miscellaneous estel's. 50 Nitrogen dcr ivati\"cs. 70 Carboxylic acid. 11 O-Methyl. 31 PllOsphate. 51 Amino. 71 Carboxylic ester. 12 O-Ethyl. 32 N itrate. 52 Acetamido. 72 Carboxylic 'Y-Iactonc. 13 O-CycIO]lCXY I. 33 Sulfate. 53 N-Glycosy!. 73 Carboxylic Ii-lactone. 14 O-Benzyl. 34 O-Tosyl. 54 Phenylhydrazine df'riyu- 74 Carboxylic amide. tive. 15 O-Phenyl. 35 O-Mesyl. 55 Oxime. 75 Carboxylic salt. 16 O-'rrityl. 36 5fi 76 Oxo derivative. 17 HemiacetaL 37 57 77 18 Aldehydro!. 38 58 78 19 39 .19 79 20 Carboxylic ester. 40 Lin kages othN than 0 or N . 60 Cycli c derivati\'(ls. 80 D eoxy. 21 O-Acel.yl. 41 Fluoride. 61 Isopropylidene. 81 Deoxyam ino. 22 O-Brnzo)'!. 42 Chloride. 62 Benzylidene. 82 D roxyacetamiclo. 23 43 B romide. 63 I-Methoxycthylidenc. 24 44 Iodide. {j4 I-Mcthoxybenzylidenc. 25 45 Mercaptal. 65 Ethylene oxide. 26 46 66 Butylene oxide. 27 47 (;7 Amylene oxide. 97 Organi c solven t of crystalliza- tion . 28 48 68 B exy lene oxide. 98 Salt of crystallization. 29 49 69 99 'Vater :)f crystallization. group have unlike configurations. Thus a D­ TABLE 3. Classification of configuration glycero- D- gluco-aldoheptose or an L-glycero-L-gluco ­ aldoheptose is classified 7a, whereas a D-glycero-L­ Ald otetrose Aldopen lose Keto hexose Related gluco-aldoheptose or an L-glycero-D-gluco-aldoheptose aldohexoses is classified 7b. The first pair of compounds as '" '0'" '0" '0" '"0 Configuration 0 Configuration 0 Configuration 0 Configuration well as the second pair are enantiomorphic, and for -0 ----- 0 0 0 evaluation of infrared absorption, do not require 2 Threose. 1 Xylose. 1 So rbose. 1 Glucose. separate code numbers. 2 Erythrose. 2 L yxose. 2 Tagatose. 2 Mannose. 3 Arabinose . 3 Fructose. 3 Galactose. 4 R ibose . 4 Psicose. 4 Talose. 5 Idose. 6 Gulose. 2.4. Configuration 7 Altrose. 8 Allose. The second digit to the right of the decimal signi­ I fies the configuration of the main structural unit, Configurations listed in table 1 are assigned numbers 2.5. Structure 1 to 8 according t o the scheme outlined in table 3_ The digit third to the right of the decimal repre­ No distinction is made between D and L modifica­ sents the characteristic structure of the substance_ tions because enantiomorphic substances give like Products containing anomeric forms in equilibrium, absorption. Racemic substances are grouped under as, for example, amOl'phous sugars and materials not 0, and compounds not covered elsewhere are classified subject to specific classification, are represented by under 9. Because the pentoses and ketohexoses 0 ; pyranose and furanose structures by 1 to 6; have one less asymmetric carbon than the aldo­ glycitols by 7 ; open-chain aldehyde and k etone hexoses, each can be considered to be related to two derivatives by 8; and aldonic acids by.9 r egardless of aldohexoses that differ in the configuration of the whether they are present as the aCId, salt, ester , terminal asymmetric carbon. On the basis of sim­ amide, or lactone. Assignment of code numbers for ilarity in properties, the pentoses and ketohexoses the pYl'anose and furanose derivatives requires are classified under configurations 1 to 4 rather than review of some problems of nomenclature and ideas 5 to 8 [3].