Binary Representation in Carbohydrate Nomenclature Clifford J. McGinn and William 6. Wheatley LeMoyne College, Syracuse. NY 13214
CHO CHO There are many instances in chemistry where, because of the presence of structural modifications, one of two possible situations may exist, for example, cis- or trans-hutene-2, cisor trans-1,2,dibromo cyclopentane, D- or L-glyceraldehyde, R- or S-2-chlorohutane. Let us consider here primarily carbohydrates, for which, over the years, many proposals for 4 5 6 7 pictorial or alphanumeric representations have been proor Dlo-aldohexose,D-galactose (14) is 0110 or oe-aldohexose, posed.l Because the elegant work of Fischer and others in and D-talose (15) is 1110 or ~ ~ ~ - a l d o h e x o s e . establishing the structure of monosaccharides involved degradation to either D- or L-glyceraldehyde, i t was natural to CHO reference the configuration of the remaining chiral centers to that of the appropriate glyceraldehyde. For example, all those monosaccharides that on degradation (the Wohl or Ruff) yielded D-glyceraldehydewere labeled D-monosaccharides. Using the original Fischer convention, the hydroxyl 8 9 10 11 groups other than the one on the next-to-last carbon atom are either "on the same side" or "on the opposite side" of the CHO CHO carbon chain. Referencing can be done simply by using binary notation. A hydroxyl to the right of the vertical bonds will be designated 0, a hydroxyl to the left will be 1. A combination of binary and decimal representations will he used. The number "2" (decimal) is thus 10 in binary; "3" is 11, "4" is 100, "5" is 101, etc. Each column represents the 12 13 14 15 base raised to a given power, and the digit is the number of Heptoses are usually named according to a combination of times the base raised to a given power contributes to the the configuration of two overlapping hexoses. For example, totalsum. For example, the number 127 hase 10 is 1X 102 2 ~10~+7~10~'.Thennmher111Obase2is1X2~+1X2~+1 X Z1 0 X ZO. In hase 10 this is 14. Using D-glyceraldehyde (1)
+
+
H-
LH -OH 1
as the primary standard, in binary notation i t is 0 (it is also 0 in decimal notation). D-Glyceraldehyde would then be described as Do-triose. The subscript following D is the binary notation translated to the hase 10. The designation of the configuration of each succeeding carbon atom as we go "up" the chain is defined by a 0 or 1 added to the left. For D-erythrose (2), and D-threose (3), CHO H--OH HO--H H--OH H--OH
tH
2 3 10 00 we have as the binary notation 00 and D-erythrose hecon~es 00 or Do-aldotetrose, and D-threose becomes 10 or DZ-aldotetrose. For the D-pentoses, D-rihose (4) is 000 or Do-aldopentose, D-arabinose (5) is 100 or Dd-aldopentose, D-xylose (6) is 010 or DZ-aldopentose,and D-xylose (7) is 110 or D6-aldopentose. For the D-hexoses, D-allose (8) is 0000 or Do-aldohexose, D-altrose (9) is 1000 or Ds-aldohexose, D-glucose (10) is 0100 or Dl-aldohexose, D-mannose (11) is 1100 or o12-aldohexose, D-gulose (12) is 0010 or DZ-aldohexose,D-idose, (13) is 1010
16 16 is D-gluco-D-guloheptulose (Fischer) or D-glycero-D-guloheptose. The carbons 2-7 have the D-glucose confignration, while carbons 1-6 have the D-gulose configuration. Using the binary notation it would he 00100, or D4-aldoheptose. Except for the unusual situation where blocking groups prevent hemiacetal (or hemiketal) formation, monosaccharides exist in the furanose or pyranose form. This of course gives rise to another chiral center. This would increase the binary notation by 16 for the 0form for the D-hexoses and remain the same for the or form. For example, a-D-glucopyranose (17) would be D~-aldohexopyranose,and the 0 form (18) would he Dzo-aldohexopyranose. CHZOH CHzOH
17 00100
18 10100
' For a recent example, see Fulkrod, J. E. J. Chem. Educ. 1989,66, 485.
Volume 67
Number 9
September 1990
747
For the D-aldohexoses the a and B forms will differ hv 16. As t o ketoses, D-fructose would he Da-2-ket~hexo~e (19), or in the cvclic form as the B anorner, D,I-2-ketohexofuranose
For disaccharides, maltose becomes 1,4-D4-aldohexopyranosvl-DL-aldohexoovranose. and sucrose would become 1.2-DA. . .. aldohexopyranosyl-DIZ-2-ketohexofnrmoside. One can appreciate further the versatility of this system of designation by considering an unusual monosaccharide such as the isomer of D-fructose in which the ketone function is in position 3. This would hecome DO-3-ketohexofuranose(assuming the 3,6-a-hemiketal form). Application to other carbohydrates, particularly mono- and disaccharides, is quite straightforward.
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748
Journal of Chemical Education
Oraanic chemists are already burdened, and some miaht even say overhurdenrd, with sytems uf nomenclnturr and rechniquei to depict configura~ions.Why propose anothern The use of a onelor two-digit number todefine the configuration of a monosaccharide completely does have something to offer. Most organic chemists who are not sugar chemists can probably draw D-glucose correctly: even mannose if they recall that these two are epimers. Beyond that, it is back to a reference hook if something like altrose or lyxose is mentioned. Translation of the suhscriot number into its hinarv notation rapidly becomes effortlks, and at this point thk configuration is defined. Obviously, the direct application of this number to monosaccharide derivatives such as reduction or oxidation products follows. Equally obvious, an even subscript refers to the D series; an odd subscript to the L series. As hemiacetals, all a-aldohexoses will have numbers between 0 and 15, and all 0-aldohexoses between 16 and 31. As pointed out earlier, the difference between the anomers will always be 16. By adopting some simple conventions, this binary notation can be adapted for use with cis and trans isomers or with (R)and (S) designations.
