One reference book lists d-mannose as being dextrorotatory; another lists it as being

How many chirality centers are contained in (a) the aldotetrose and (b) the ketopentose Practice Problem 22.1 just given? (c) How many stereoisomers would you expect from each general structure?

Write three-dimensional formulas for each aldotetrose and ketopentose isomer in Practice Problem 22.1 and designate each as a d or l sugar.

Draw the b-pyranose form of (a) in its lowest energy chair conformation, and a Fischer Practice Problem 22.3 projection for (b).

(a) What products would be formed if salicin were treated with dilute aqueous HCl? (b) Outline a mechanism for the reactions involved in their formation.

How would you convert d-glucose to a mixture of ethyl a-d-glucopyranoside and ethyl b-d-glucopyranoside? Show all steps in the mechanism for their formation.

How might you distinguish between a-d-glucopyranose (i.e., d-glucose) and methyl Practice Problem 22.6 a-d-glucopyranoside?

(a) Would you expect d-glucaric acid to be optically active? (b) Write the open-chain structure for the aldaric acid (mannaric acid) that would be obtained by nitric acid oxidation of d-mannose. (c) Would you expect mannaric acid to be optically active? (d) What aldaric acid would you expect to obtain from d-erythrose? H OH H OH CHO CH2OH D-Erythrose (e) Would the aldaric acid in (d) show optical activity? (f) d-Threose, a diastereomer of d-erythrose, yields an optically active aldaric acid when it is subjected to nitric acid oxidation. Write Fischer projection formulas for d-threose and its nitric acid oxidation product. (g) What are the names of the aldaric acids obtained from d-erythrose and d-threose?

d-Glucaric acid undergoes lactonization to yield two different g-lactones. What are their structures?

What products would you expect to be formed when each of the following compounds is treated with an appropriate amount of periodic acid? How many molar equivalents of HIO4 would be consumed in each case? (a) 2,3-Butanediol (b) 1,2,3-Butanetriol (c) HO OH OCH3 OCH3 (d) HO O OH (e) O O OH (f) cis-1,2-Cyclopentanediol (g) HO OH (h) d-Erythrose

(a) Would you expect d-glucitol to be optically active? (b) Write Fischer projection Practice Problem 22.11 formulas for all of the d-aldohexoses that would yield optically inactive alditols.

Although d-fructose is not an epimer of d-glucose or d-mannose (d-fructose is a ketohexose), all three yield the same phenylosazone. (a) Using Fischer projection formulas, write an equation for the reaction of fructose with phenylhydrazine. (b) What information about the stereochemistry of d-fructose does this experiment yield?

(a) What are the structures of l-(+)-threose and l-(+)-erythrose? (b) What aldotriose Practice Problem 22.13 would you use to prepare them in a KilianiFischer synthesis?

(a) Outline a KilianiFischer synthesis of epimeric aldopentoses starting with d-(-)-erythrose (use Fischer projections). (b) The two epimeric aldopentoses that one obtains are d-(-)-arabinose and d-(-)-ribose. Nitric acid oxidation of d-(-)-ribose yields an optically inactive aldaric acid, whereas similar oxidation of d-(-)-arabinose yields an optically active product. On the basis of this information alone, which Fischer projection represents d-(-)-arabinose and which represents d-(-)-ribose?

Subjecting d-(-)-threose to a KilianiFischer synthesis yields two other epimeric aldopentoses, d-(+)-xylose and d-(-)-lyxose. d-(+)-Xylose can be oxidized (with nitric acid) to an optically inactive aldaric acid, while similar oxidation of d-(-)-lyxose gives an optically active product. What are the structures of d-(+)-xylose and d-(-)-lyxose?

There are eight aldopentoses. In Practice Problems 22.14 and 22.15 you have arrived at the structures of four. What are the names and structures of the four that remain?

The aldohexose d-(+)-galactose can be obtained by hydrolysis of lactose, a disaccharide found in milk. When d-(+)-galactose is treated with nitric acid, it yields an optically inactive aldaric acid. When d-(+)-galactose is subjected to Ruff degradation, it yields d-(-)-lyxose (see Practice Problem 22.15). Using only these data, write the Fischer projection formula for d-(+)-galactose.

Fischer actually had to subject both g-lactones of d-glucaric acid (Practice Problem 22.8) Practice Problem 22.18 to the procedure just outlined. What product does the other g-lactone yield?

Direct oxidation of an aldose affects the aldehyde group first, converting it to a carboxylic acid (Section 22.6B), and most oxidizing agents that will attack 18 alcohol groups will also attack 28 alcohol groups. Clearly, then, a laboratory synthesis of a uronic acid from an aldose requires protecting these groups from oxidation. Keeping this in mind, suggest a method for carrying out a specific oxidation that would convert d-galactose to d-galacturonic acid. (Hint: See Section 22.5E.)

Draw conformational formulas for each of the following: (a) a-d-allopyranose, (b) methyl b-d-allopyranoside, and (c) methyl 2,3,4,6-tetra-O-methyl-b-d-allopyranoside.

Draw structures for furanose and pyranose forms of d-ribose. Show how you could use periodate oxidation to distinguish between a methyl ribofuranoside and a methyl ribopyranoside.

One reference book lists d-mannose as being dextrorotatory; another lists it as being levorotatory. Both references are correct. Explain.

The starting material for a commercial synthesis of vitamin C is l-sorbose (see the following reaction); it can be synthesized from d-glucose through the following reaction sequence: D-Glucose D-Glucitol L-Sorbose H2 Ni O2 Acetobacter suboxydans HO H OH H OH HO O H OH The second step of this sequence illustrates the use of a bacterial oxidation; the microorganism A. suboxydans accomplishes this step in 90% yield. The overall result of the synthesis is the transformation of a d-aldohexose (d-glucose) into an l-ketohexose (l-sorbose). What does this mean about the specificity of the bacterial oxidation?

What two aldoses would yield the same phenylosazone as l-sorbose (Problem 22.24)?

In addition to fructose (Practice Problem 22.12) and sorbose (Problem 22.24), there are two other 2-ketohexoses, psicose and tagatose. d-Psicose yields the same phenylosazone as d-allose (or d-altrose); d-tagatose yields the same osazone as d-galactose (or d-talose). What are the structures of d-psicose and d-tagatose?

A, B, and C are three aldohexoses. Compounds A and B yield the same optically active alditol when they are reduced with hydrogen and a catalyst; A and B yield different phenylosazones when treated with phenylhydrazine; B and C give the same phenylosazone but different alditols. Assuming that all are d sugars, give names and structures for A, B, and C.

Xylitol is a sweetener that is used in sugarless chewing gum. Starting with an appropriate monosaccharide, outline a possible synthesis of xylitol.

Although monosaccharides undergo complex isomerizations in base (see Section 22.5A), aldonic acids are epimerized specifically at C2 when they are heated with pyridine. Show how you could make use of this reaction in a synthesis of d-mannose from d-glucose.

(a) Heating d-altrose with dilute acid produces a nonreducing anhydro sugar (C6H10O5). Methylation of the anhydro sugar followed by acid hydrolysis yields 2,3,4-tri-O-methyl-d-altrose. The formation of the anhydro sugar takes place through a chair conformation of b-d-altropyranose in which the iCH2OH group is axial. What is the structure of the anhydro sugar, and how is it formed? (b) d-Glucose also forms an anhydro sugar but the conditions required are much more drastic than for the corresponding reaction of d-altrose. Explain.

Show how the following experimental evidence can be used to deduce the structure of lactose (Section 22.12D): 1. Acid hydrolysis of lactose (C12H22O11) gives equimolar quantities of d-glucose and d-galactose. Lactose undergoes a similar hydrolysis in the presence of a b-galactosidase. 2. Lactose is a reducing sugar and forms a phenylosazone; it also undergoes mutarotation. 3. Oxidation of lactose with bromine water followed by hydrolysis with dilute acid gives d-galactose and d-gluconic acid. 4. Bromine water oxidation of lactose followed by methylation and hydrolysis gives 2,3,6-tri-O-methylgluconolactone and 2,3,4,6-tetra-O-methyl-d-galactose. 5. Methylation and hydrolysis of lactose give 2,3,6-tri-O-methyl-d-glucose and 2,3,4,6-tetra-O-methyl-d-galactose.

Deduce the structure of the disaccharide melibiose from the following data: 1. Melibiose is a reducing sugar that undergoes mutarotation and forms a phenylosazone. 2. Hydrolysis of melibiose with acid or with an a-galactosidase gives d-galactose and d-glucose. 3. Bromine water oxidation of melibiose gives melibionic acid. Hydrolysis of melibionic acid gives d-galactose and d-gluconic acid. Methylation of melibionic acid followed by hydrolysis gives 2,3,4,6-tetra-O-methyl-d-galactose and 2,3,4,5-tetra-O-methyl-d-gluconic acid. 4. Methylation and hydrolysis of melibiose give 2,3,4,6-tetra-O-methyl-d-galactose and 2,3,4-tri-O-methyl-d-glucose.

Trehalose is a disaccharide that can be obtained from yeasts, fungi, sea urchins, algae, and insects. Deduce the structure of trehalose from the following information: 1. Acid hydrolysis of trehalose yields only d-glucose. 2. Trehalose is hydrolyzed by a-glucosidase but not by b-glucosidase enzymes. 3. Trehalose is a nonreducing sugar; it does not mutarotate, form a phenylosazone, or react with bromine water. 4. Methylation of trehalose followed by hydrolysis yields two molar equivalents of 2,3,4,6-tetra-O-methyl-d-glucose.

Outline chemical tests that will distinguish between members of each of the following pairs: (a) d-Glucose and d-glucitol (b) d-Glucitol and d-glucaric acid (c) d-Glucose and d-fructose (d) d-Glucose and d-galactose (e) Sucrose and maltose (f) Maltose and maltonic acid (g) Methyl b-d-glucopyranoside and 2,3,4,6-tetra-O-methyl-b-d-glucopyranose (h) Methyl a-d-ribofuranoside (I) and methyl 2-deoxy-a-d-ribofuranoside (II):

A group of oligosaccharides called Schardinger dextrins can be isolated from Bacillus macerans when the bacillus is grown on a medium rich in amylose. These oligosaccharides are all nonreducing. A typical Schardinger dextrin undergoes hydrolysis when treated with an acid or an a-glucosidase to yield six, seven, or eight molecules of d-glucose. Complete methylation of a Schardinger dextrin followed by acid hydrolysis yields only 2,3,6-tri-O-methyl-d-glucose. Propose a general structure for a Schardinger dextrin.

Isomaltose is a disaccharide that can be obtained by enzymatic hydrolysis of amylopectin. Deduce the structure of isomaltose from the following data: 1. Hydrolysis of 1 mol of isomaltose by acid or by an a-glucosidase gives 2 mol of d-glucose. 2. Isomaltose is a reducing sugar. 3. Isomaltose is oxidized by bromine water to isomaltonic acid. Methylation of isomaltonic acid and subsequent hydrolysis yields 2,3,4,6-tetra-O-methyl-d-glucose and 2,3,4,5-tetra-O-methyl-d-gluconic acid. 4. Methylation of isomaltose itself followed by hydrolysis gives 2,3,4,6-tetra-O-methyl-d-glucose and 2,3,4-tri-O-methyl-d-glucose.

Stachyose occurs in the roots of several species of plants. Deduce the structure of stachyose from the following data: 1. Acidic hydrolysis of 1 mol of stachyose yields 2 mol of d-galactose, 1 mol of d-glucose, and 1 mol of d-fructose. 2. Stachyose is a nonreducing sugar. 3. Treating stachyose with an a-galactosidase produces a mixture containing d-galactose, sucrose, and a nonreducing trisaccharide called raffinose. 4. Acidic hydrolysis of raffinose gives d-glucose, d-fructose, and d-galactose. Treating raffinose with an a-galactosidase yields d-galactose and sucrose. Treating raffinose with invertase (an enzyme that hydrolyzes sucrose) yields fructose and melibiose (see Problem 22.33). 5. Methylation of stachyose followed by hydrolysis yields 2,3,4,6-tetra-O-methyl-d-galactose, 2,3,4-tri-O-methyl-d-galactose, 2,3,4-tri-O-methyl-d-glucose, and 1,3,4,6-tetra-O-methyl-d-fructose.

Arbutin, a compound that can be isolated from the leaves of barberry, cranberry, and pear trees, has the molecular formula C12H16O7. When arbutin is treated with aqueous acid or with a b-glucosidase, the reaction produces d-glucose and a compound X with the molecular formula C6H6O2. The 1 H NMR spectrum of compound X consists of two singlets, one at d 6.8 (4H) and one at d 7.9 (2H). Methylation of arbutin followed by acidic hydrolysis yields 2,3,4,6-tetra-O-methyl-d-glucose and a compound Y (C7H8O2). Compound Y is soluble in dilute aqueous NaOH but is insoluble in aqueous NaHCO3. The 1 H NMR spectrum of Y shows a singlet at d 3.9 (3H), a singlet at d 4.8 (1H), and a multiplet (that resembles a singlet) at d 6.8 (4H). Treating compound Y with aqueous NaOH and (CH3)2SO4 produces compound Z (C8H10O2). The 1 H NMR spectrum of Z consists of two singlets, one at d 3.75 (6H) and one at d 6.8 (4H). Propose structures for arbutin and for compounds X, Y, and Z

Figure 22.21 shows the 13C NMR spectrum for the product of the reaction of d-(+)-mannose with acetone containing a trace of acid. This compound is a mannofuranose with some hydroxyl groups protected as acetone acetals (as acetonides). Use the 13C NMR spectrum to determine how many acetonide groups are present in the compound.

Figure 22.21 shows the 13C NMR spectrum for the product of the reaction of d-(+)-mannose with acetone containing a trace of acid. This compound is a mannofuranose with some hydroxyl groups protected as acetone acetals (as acetonides). Use the 13C NMR spectrum to determine how many acetonide groups are present in the compound.

Of the two anomers of methyl 2,3-anhydro-d-ribofuranoside, I, the b form has a strikingly lower boiling point. Suggest an explanation using their structural formulas.

The following reaction sequence represents an elegant method of synthesis of 2-deoxy-d-ribose, IV, published by D. C. C. Smith in 1955: H OH H H H OH D-Glucose H OH OH OH HO H H OH H OH anhydrous CuSO4 CH3SO2Cl C5H5N HO H2O H H O O H O O II IV [III] H3O O H O H O O H OH (a) What are the structures of II and III? (b) Propose a mechanism for the conversion of III to IV.

acetic anhydride anhydrous sodium acetate acetic anhydride cat. HA D-Glucose D-Glucopyranose pentaacetate, anomer V D-Glucopyranose pentaacetate, anomer VI The 1 H NMR data for the two anomers included very comparable peaks in the d 2.05.6 region but differed in that, as their highest d peaks, anomer V had a doublet at d 5.8 (1H, J = 12 Hz) while anomer VI had a doublet at d 6.3 (1H, J = 4 Hz). (a) Which proton in these anomers would be expected to have these highest d values? (b) Why do the signals for these protons appear as doublets? (c) The relationship between the magnitude of the observed coupling constant and the dihedral angle (when measured using a Newman projection) between C i H bonds on the adjacent carbons of a C i C bond is given by the Karplus equation. It indicates that an axialaxial relationship results in a coupling constant of about 9 Hz (observed range is 814 Hz) and an equatorialaxial relationship results in a coupling constant of about 2 Hz (observed range is 17 Hz). Which of V and VI is the a anomer and which is the b anomer? (d) Draw the most stable conformer for each of V and VI.

(a) The members of one class of low-calorie sweeteners are called polyols. The chemical synthesis of one such polyol sweetener involves reduction of a certain disaccharide to a mixture of diastereomeric glycosides. The alcohol (actually polyol) portion of the diastereomeric glycosides derives from one of the sugar moieties in the original disaccharide. Exhaustive methylation of the sweetener (e.g., with dimethyl sulfate in the presence of hydroxide) followed by hydrolysis would be expected to produce 2,3,4,6-tetra-O-methyl-a-dglucopyranose, 1,2,3,4,5-penta-O-methyl-d-sorbitol, and 1,2,3,4,5-penta-O-methyl-d-mannitol, in the ratio of 2:1:1. On the basis of this information, deduce the structure of the two disaccharide glycosides that make up the diastereomeric mixture in this polyol sweetener. (b) Knowing that the mixture of two disaccharide glycosides in this sweetener results from reduction of a single disaccharide starting material (e.g., reduction by sodium borohydride), what would be the structure of the disaccharide reactant for the reduction step? Explain how reduction of this compound would produce the two glycosides. (c) Write the lowest energy chair conformational structure for 2,3,4,6-tetra-O-methyl-a-d-glucopyranose.

Shikimic acid is a key biosynthetic intermediate in plants and microorganisms. In nature, shikimic acid is converted to chorismate, which is then converted to prephenate, ultimately leading to aromatic amino acids and other essential plant and microbial metabolites (see the Chapter 21 Learning Group problem). In the course of research on biosynthetic pathways involving shikimic acid, H. Floss (University of Washington) required shikimic acid labeled with 13C to trace the destiny of the labeled carbon atoms in later biochemical transformations. To synthesize the labeled shikimic acid, Floss adapted a synthesis of optically active shikimic acid from d-mannose reported earlier by G. W. J. Fleet (Oxford University). This synthesis is a prime example of how natural sugars can be excellent chiral starting materials for the chemical synthesis of optically active target molecules. It is also an excellent example of classic reactions in carbohydrate chemistry. The FleetFloss synthesis of d-(-)-[1,7-13C]-shikimic acid (1) from d-mannose is shown in Scheme 1. (a) Comment on the several transformations that occur between d-mannose and 2. What new functional groups are formed? (b) What is accomplished in the steps from 2 to 3, 3 to 4, and 4 to 5? (c) Deduce the structure of compound 9 (a reagent used to convert 5 to 6), knowing that it was a carbanion that displaced the trifluoromethanesulfonate (triflate) group of 5. Note that it was compound 9 that brought with it the required 13C atoms for the final product. (d) Explain the transformation from 7 to 8. Write out the structure of the compound in equilibrium with 7 that would be required for the process from 7 to 8 to occur. What is the name given to the reaction from this intermediate to 8? (e) Label the carbon atoms of d-mannose and 1 by number or letter so as to show which atoms in 1 came from which atoms of d-mannose.