CARBOHYDRATE PART 1

Configuration of Aldose

An Aldose' contains an aldehyde with two or more hydroxyl groups attached; one of the hydroxyl groups is at end opposite to the aldehyde. The L and D symbols apply to the two different configurations of the asymmetric carbon farthest from the aldehyde group. Aldoses can have three or more carbons

Acylation

Acylation of hydroxyl groups of carbohydrates is one of the most commonly used functional group protection techniques in the synthesis of oligosaccharides.

Alkylation

The -OH groups in carbohydrates react readily with alkylating agents to give ethers via a simple SN2 reaction. Methylation can be achieved using methyl iodide, CH3I, and silver oxide Ag2O.

Oxidation

Nucleophilic Addition to C=O. Aldehydes, RCHO, can be oxidised to carboxylic acids, RCO2H. Ketones are not oxidised under these conditions as they lack the critical H for the elimination to occur (see mechanism below). The reactive species in the oxidation is the hydrate formed when the aldehyde reacts with the water.

Reduction

1. reduce use NaBH4

2. reduce to COOH on both side use HNO3

Nitric acid is a strong acid and is a potent oxidant, but its salts are rather unreactive. Under strongly acidic conditions, it converts primary alcoholic and aldehydic groups into carboxylic acid groups.