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Chapter 23: Q28P (page 1229)

Predict the products formed when the following sugars react with excess acetic anhydride and pyridine.

  1. 伪-顿-驳濒耻肠辞辫测谤补苍辞蝉别
  2. 尾-顿-谤颈产辞蹿耻谤补苍辞蝉别

Short Answer

Expert verified
  1. penta-O-acetyl-伪-顿-驳濒耻肠辞辫测谤补苍辞蝉别
  2. tetra-O-acetyl-尾-顿-谤颈产辞蹿耻谤补苍辞蝉别


Step by step solution

01

Formation of acetate esters

The hydroxy (-OH) groups of a sugar can be converted to acetate esters by the treatment with acetic anhydride and pyridine. The stereochemistry is usually retained at the anomeric carbon.

02

Pyranose and furanose

Pyranose is a six-membered cyclic hemiacetal while a furanose is a five-membered cyclic hemiacetal.

03

Formation of product

  1. 伪-顿-驳濒耻肠辞辫测谤补苍辞蝉别 on treatment with excess acetic anhydride and pyridine gives penta-O-acetyl-伪-D-glucopyranoside as the product.

    Reaction
  2. 尾-顿-谤颈产辞蹿耻谤补苍辞蝉别 on treatment with excess acetic anhydride and pyridine gives tetra-O-acetyl-尾-D-ribofuranoside as the product.

    Reaction

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Most popular questions from this chapter

An important protecting group developed specifically for polyhydroxy compounds like nucleosides is the tetraisopropyl-disiloxanyl group, abbreviated TIPDS, that can protect two alcohol groups in a molecule.

(a) The TIPDS group is somewhat hindered around the Siatoms by the isopropyl groups. Which OHis more likely to react first with TIPDS chloride? Show the product with the TIPDS group on one oxygen.

(b) Once the TIPDS group is attached at the first oxygen, it reaches around to the next closest oxygen. Show the final product with two oxygens protected.

(c) The unprotected hydroxy group can now undergo reactions without affecting the protected oxygens. Show the product after the protected nucleoside from (b) is treated with tosyl chloride and pyridine, followed by NaBr, ending with deprotection with Bu4NF.

Fructose is found in many fruits. From memory, draw fructose in

  1. the Fischer projection of the open chain.
  2. The most stable chair conformation of the most stable pyranose anomer.
  3. The Haworth projection of the most stable pyranose anomer

Which of the following sugars are reducing sugars? Comment on the common name sucrose for table sugar.

(a) methyl伪鈥�D鈥�galactopyranoside (b) 尾鈥�L鈥�idopyranose (an aldohexose)

(c) 伪鈥�D鈥�allopyranose (d) 尾鈥�L鈥�ribofuranoside

(e) (f)

The relative configurations of the stereoisomers of tartaric acid were established by the following synthesis:

(1) D-(+)-glyceraldehydediastereomers A and B (separated)

(2) Hydrolysis of A and B using aqueous Ba(OH)2 gave C and D, respectively.

(3) HNO3 oxidation of C and D gave (-)-tartaric acid and meso-tartaric acid, respectively.

(a) You know the absolute configuration of D-(+)-glyceraldehyde, Use Fischer projections to show the absolute configurations of products A, B, C, and D.

(b) Show the absolute configurations of the three stereoisomers of tartaric acid: (+)-tartaric acid, (-)-tartaric acid, and meso-tartaric acid.

Draw and name the enantiomers of the sugars shown in Figure 23-2. Give the relative configuration (D or L) and the sign of the rotation in each case.
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