CHEM 334 Chapter 23: Carbohydrates and Nucleic Acids

Sugar naming conventions

• D &L - chiral carbon farthest from the carbonyl determines if molecule is D or L; if OH is on the right = D, if OH group on left = L

• +/- If DL determining OH group is on the same side as the previous Carbon, it is + if on opposing side then -

• Backbone to 3D - If OH group is on the right it will be pointing down, if the OH group is on the left it will be pointing up

• Alpha and beta - Alpha refers to the anomeric Carbon OH group; if it points down it is alpha and up is beta

Base-catalyzed epimerization of glucose

Sugar + OH- → H2O →Final OH group switches sides (eg. from left to right and vice versa)

Enediol rearrangement

Sugar + OH- + H2O → CHO group moves down the backbone; this can occur continuously

Reduction of simple sugars

Sugar + NaBH4 (or H2/Ni) → reduces CHO group into CH2O group (forms epimers)

Oxidation by bromine

Sugar + Br2 + H2O → turns CHO group into COOH

Oxidation by nitric acid

Sugar + HNO3 → turns CHO and opposite terminal CH2OH into COOH group (stronger oxidizing agent than Br)

Oxidation by Tollens reagent

Sugar + Ag(NO3)2OH → turns CHO group into carboxylate COO- + silver mirror

Glycosides

Non-reducing sugars that do not react with Tollens reagents, anomeric carbon is bonded to a non OH group (eg. O-CH3)

Glycoside formations

Sugar + CH3OH, H+ → methyl group replaces H on anomeric OH, alpha position is slightly favored due to LP steric hinderance

Glycoside to hemiacetal

Sugar + H2O, H+ → turns glycoside into hemiacetal

Methyl ether formations

Sugar + CH3I, Ag2O in excess → ALL OH groups become O-CH3

Acetate ester formation

Sugar + anhydride + pyridine (xs) → replaces all OH groups with O - ketone

Ruff degradation

Sugar + Br2, H2O → CHO replaced with COOH + H2o2 + Fe(SO4)3 → Shortens carbon chain by one + release of CO2

Kilian-Fischer synthesis

Sugar + KCN, HCN → turns CHO into a CH2O group and adds a CN; + H2, PdBaso4 (LINDLAR CATALYST) → H3O+ turns CN group into H-C=N-H; + H3O+ → replaces nitro group with CHO, lengthen chain by 1 C

Osazone formation

Sugar + H2N-NH-Ph, H+ → C1 and C2 replaced with C=N-NH-Ph groups