Abstract
Treatment of D‐ribose with chloral in the presence of acid catalyst gives 1,2‐O‐(S)‐trichloroethylidene‐α‐D‐ribofuranose (1) (β‐ribochloralose). Some derivatives of this product (1) were synthesized to be used as an intermediate in carbohydrate chemistry. Tricyclic orthoester structure (3, 77%) was obtained from the reaction of 1 with potassium t‐butoxide. This novel orthoester is expected to be useful as a glycosyl donor in the formations of new ribofuranoside units. 3‐O‐Methyl‐ribochloralose (5) was synthesized in 75% yield via the methylation of 1. 5‐O‐Tosyl‐ribochloralose (6, 61%) was prepared with monotosylation reaction of 1. Treatment of 6 with NaN3 in DMF gives a 5‐azido‐5‐deoxy‐ribochloralose (7) in 77% yield. The azidosugar (7) was reduced to 5‐amino‐5‐deoxy‐ribochloralose (8, 72%) with triphenylphosphine according to Staudinger’s reduction procedure.
Highlights
Chloraloses are known as chloral derivatives of pentoses and hexoses
The first members of this class are α- and βchloralose prepared via the reaction of anhydrous glucose and anhydrous chloral in the presence of sulfuric acid catalyst by Heffter [1] and the first time applied to therapeutics by Hanriot [2, 3]
Results and Discussion d-Ribose as a starting material was treated with catalytic amounts of sulfuric acid in chloral for 2 h under reflux to give 1,2-O-(S)-trichloroethylidene-α-d-ribofuranose (1) (β-ribochloralose) which was isolated via crystallization (Scheme 1)
Summary
Chloraloses are known as chloral derivatives of pentoses and hexoses. The first members of this class are α- and βchloralose (or -glucochloralose) prepared via the reaction of anhydrous glucose and anhydrous chloral in the presence of sulfuric acid catalyst by Heffter [1] and the first time applied to therapeutics by Hanriot [2, 3]. 1,2-O-trichloroethylidene acetals are very stable protecting group under acidic media because of inductive effects of trichloromethyl group and stable in mild basic conditions. It is unstable against strong bases such as potassium tert-butoxide and is converted to most reactive ketene acetals [5, 9]. The most famous chloralose, (R)-1,2-Otrichloroethylidene-α-d-glucofuranose or α-chloralose, is a commercially available product and possesses anesthetic and hypnotic effects [2, 11] It has been widely used as a rodenticide [12], bird repellent, and veterinary drug [11, 13, 14]. Anesthetic properties of all stereoisomers for arabinochloralose were investigated and β-d-arabinochloralose was found to be more reactive than others [15]
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