A Mnemonic Scheme for Interconverting Fischer Projections of Open-Chain Monosaccharides and Haworth Projections of Corresponding a-and 8-Anomerie Forms Monosaccharides generally exist in solution as an equilibrium mixture of a cyclic hemiacetal or hemiketal a- and 8anomera and the corresponding open-chain form.' While a variety of schemes exist for drawing Haworth projections of cyclic monosaccharides, given the open-chain form in a Fischer projection, none employs aids to facilitate memori~ation.~ I have developed a simple set of rulesfor drawing Haworth projections of a - and 0-anomericforms of monosaccharides. As these rules are based on a whimsical but meaningful set of mnemonic keys, students grasp and remember them very readily. For alliterative effect, I call them Mitschele Mnemonics. They are as follows:
1. Start the ring with the anomeric carbon on the right, and continue to draw the remainingatoms in the ring in a clockwise direction, ending with the ring oxygen a t the top of the drawing. 2. Hydroxyl groups in the right (Dextro-) are drawn Down; those on the left (Leuo-) Leuitate up. 3. The last -CH20H group is drawn heLow for an L-sugar; above for a D-sugar. 4. The hydroxyl groupattached to theanomeric carbon and thelast -CH20H groupare drawnBath on thesameside of the ring for the 8-anomer; for the a-anomer each is Alone. Students tell me that these rules make it easv for them to recoenize a- and B-anomers and the D and L - forms of monmaccharidcs in their Haworth pro~ections.They also find it simple to use there rules in re,,erre: to draw Fischer projections of the open.rhain form o l e monosaccharide. given the corresponding Hawonh projection of the ring form. ~
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S e e , for example. Wade, L. G.. Jr. Organic Chemisw: Prentlar-Hall: Englewood Cllffs. KI. 1987;Sect. 259D. See, for example. Wheeler, D. M. S.: Wheeler. M. M.: Wheeler. T. S. J. Chem. Educ. 1982, 59, 969-970: or Wade. L. G.. Jr. Orgenic ChemIsfry;Prentlce-Hall: Englewwd Cliffs. NJ. 1987: Sect. 25-3D. Jonathan MHschele Saint Joseph's College Windham. ME 04062
Volume 67
Number 7 July 1990
553
