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Chapter 23: Q26P (page 1228)

Question: Propose a mechanism for methylation of any one of the hydroxy groups of methyl-α-D-glucopyranoside,using and dimethyl sulfate.

Short Answer

Expert verified

The most common method for forming simple ethers is the Williamson ether synthesis that involves a strongly basic alkoxide ion. A sugar is believed to be iosmerized and decomposed under these basic conditons.

Step by step solution

01

Step-by-Step solutionStep 1: Ether formation

The most common method for forming simple ethers is the Williamson ether synthesis that involves a strongly basic alkoxide ion. A sugar is believed to be iosmerized and decomposed under these basic conditons.

02

Mechanism

From modified Williamson method, it is known that a sugar can be first converted to a glycoside by the treatment with an alcohol and an acid catalyst. Since glycoside is an acetal, therefore it is stable to base. Further treatment of glycoside with sodium hydroxide and dimethyl sulfate yields the methylated carbohydrate.

Mechanism for methylation of any one of the hydroxy groups

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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?

Use fig. 23-3 (the D-family of aldoses) to name the following aldoses.

(a) The C2 epimer of D-xylose

(b) The C3 epimer of D-erythrose

(c) The C3 epimer of D-altros

(d) The enantiomer of D-talose

(e) The C-5 epimer of D-idose

Question. Retroviruses like HIV, the pathogen responsible for AIDS, incorporate an RNA template that is copied into DNA during infection. The reverse transcriptaseenzyme that copies RNA into DNA is relatively nonselective and error-prone, leading to a high mutation rate. Its lack of selectivity is exploited by the anti-HIV drug AZT (3’-azido-2’,3’-dideoxythymidine), which becomes phosphorylated and is incorporated by reverse transcriptase into DNA, where it acts as a chain terminator. Mammalian DNA polymerases are more selective, having a low affinity for AZT, so its toxicity is relatively low.

  1. Draw the structures of AZT and natural deoxythymidine.
  2. Draw the structure of AZT 5’-triphosphate, the derivative that inhibits reverse transcriptase.

Like glucose, galactose mutarotates when it dissolves in water. The specific rotation of α-D-galactopyranoseis +150.70 , and that of the β anomer is +52.80 . When either of the pure anomers dissolves in water, the specific rotation gradually changes to +80.20. Determine the percentages of the two anomers present at equilibrium.

Draw the structures of the compounds named in Problem 23-20 parts (a), (c), and (d). Allose is the C3 epimer of glucose and ribose is the C2 epimer of arabinose.
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