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Chapter 23: Q11P (page 1218)

The carbonyl group in D-galactose may be isomerized from C1 to C2 by brief treatment with dilute base (by enediol rearrangement, Section 23-7). The product is the C4 epimer of fructose. Draw the furanose structure of the product.

Short Answer

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furanose structure of the product

Step by step solution

01

Epimers

Sugars which have the common configuration like the arrangement of H - and - OH around carbon atoms are same except the carbon present at α position or carbon number 2 are known as epimers. For example, glucose and mannose are epimers of each other.

02

Fructose

Fructose is a ketohexose which contain a ketone group. It is used as a sweetening agent in many confectionaries and also as a substitute of cane sugar.

03

Furanose

Furanose is a five-membered cyclic hemiacetal whose name is derived from the five-membered cyclic ether furan. Five membered ring of fructose is known as fructofuranose.

04

The reaction forming the furanose structure

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Most popular questions from this chapter

Erwin Chargaff’s discovery that DNA contains equimolar amounts of guanine and cytosine and also equimolar amounts of adenine and thymine has come to be known as Chargaff’s rule:

G = C and A = T

(a) Does Chargaff’s rule imply that equal amounts of guanine and adenine are present in DNA? That is, does G = A?

(b) Does Chargaff’s rule imply that the sum of the purine residues equals the sum of the pyrimidine residues? That is, does A + G = C + T?

(c) Does Chargaff’s rule apply only to double-stranded DNA, or would it also apply to each individual strand if the double helical strand were separated into its two complementary strands?

Question: Exposure to nitrous acid (see Section 19-16), sometimes found in cells, can convert cytosine to uracil.

  1. Propose a mechanism for this conversion.
  2. Explain how this conversion would be mutagenic upon replication.
  3. DNA generally includes thymine, rather than uracil(found in RNA). Based on this fact, explain why the nitrous acid-induced mutation of cytosine to uracil is more easily repaired in DNA than it is in RNA.

Some protecting groups can block two OH groups of a carbohydrate at the same time. One such group is shown here, protecting the 4-OH and 6-OH groups of β -D-glucose.

(a) What type of functional group is involved in this blocking group?

(b) What did glucose react with to form this protected compound?

(c) When this blocking group is added to glucose, a new chiral center is formed. Where is it? Draw the stereoisomer that has the other configuration at this chiral center. What is the relationship between these two stereoisomers of the protected compound?

(d) Which of the two stereoisomers in part (c) do you expect to be the major product? Why?

(e) A similar protecting group, called an acetonide, can block reaction at the 2′ and 3′ oxygens of a ribonucleoside. This protected derivative is formed by the reaction of the nucleoside with acetone under acid catalysis. From this information, draw the protected product formed by the reaction.

(a) Which of the D-aldopentoses will give optically active aldaric acids on oxidation with HNO3 ?

(b) Which of the D-aldotetroses will give optically active aldaric acids on oxidation withHNO3 ?

(c) Sugar X is known to be a D-aldohexose. On oxidation with HNO3 , X gives an optically inactive aldaric acid. When X is degraded to an aldopentose, oxidation of the aldopentose gives an optically active aldaric acid. Determine the structure of X.

(d) Even though sugar X gives an optically inactive aldaric acid, the pentose formed by degradation gives an optically active aldaric acid. Does this finding contradict the principle that optically inactive reagents cannot form optically active products?

(e) Show what products results if the aldopentose formed from degradation of X is further degraded to an aldotetrose. DoesHNO3 oxidize this aldotetrose to an optically active aldaric acid?

Without referring to the chapter, draw the chair conformation of

(a) α -D-mannopyranose (the C2 epimer of glucose).

(b) β -D-allopyranose (the C3 epimer of glucose.)

(c) α -D-galactopyranose (the C4 epimer of glucose).

(d) N-formylglucosamine, glucose with C2 oxygen atom replaced by a formylated amino group.
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