Benzimidazole

by Javad
(Canada)

Original Text:

Benzimidazoles are very useful intermediates /subunits for the development of molecules of pharmaceutical or biological interest. Substituted benzimidazole derivatives have found aplications in diverse therapeutic areas including antiulcers, antihypertensives, antivirals, antifungals, anticancers, and antihistaminics to name Just a few.1–3
The traditional synthesis of benzimidazoles involves the reaction between an ortho-phenylenediamine and a carboxylic acid or its derivatives (nitriles, amidates, orthoesters) under harsh dehydrating conditions.4 Benzimidazoles have also been prepared on solid-phase to provide a combinatorial approach.5 The most popular strategies for their synthesis utilize o-nitroanilines as intermediates or resort to direct N-alkylation of an unsubstituted benzimidazole.6 A number of synthetic protocols that involve intermediate o-nitroanilines have evolved to include the synthesis of benzimidazoles on solid support.7 Another method for the synthesis of these compounds is the reaction of o- henylenediamine with aldehydes in the presence of acidic catalysts under various reaction conditions.8,9 However, many of these methods have several drawbacks such as low yields, use of expensive reagents, a special oxidation process or long reaction times, tedious work-up procedures, co-occurrence of several side reactions and poor selectivity.
Therefore, the search continues for a better catalyst for the synthesis of benzimidazoles in terms of operational
simplicity, economic viability and in particular, with greater selectivity. 10

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Revised Text:

Benzimidazoles are very useful intermediates/subunits in developing molecules of pharmaceutical or biological interest. Substituted benzimidazole derivatives have found aplications in diverse therapeutic areas including; anti-ulcers, anti-hypertensives, anti-virals, anti-fungals, anti-cancers, and antihistaminics, to name just a few. 1–3

The traditional synthesis of benzimidazoles involves the reaction between an ortho-phenylenediamine and a carboxylic acid or its derivatives (nitriles, amidates, orthoesters) under harsh dehydrating conditions.4

Benzimidazoles have also been prepared on solid-phase to provide a combinatorial approach. 5 The most popular strategies for their synthesis utilize o-nitroanilines as intermediates or resort to direct N-alkylation of an unsubstituted benzimidazole. 6 A number of synthetic protocols that involve intermediate o-nitroanilines, have evolved to include the synthesis of benzimidazoles on solid support. 7

Another method for the synthesis of these compounds is the reaction of o-henylenediamine with aldehydes in the presence of acidic catalysts under various reaction conditions. 8,9 However, many of these methods have drawbacks such as; low yields, use of expensive reagents, a special oxidation process or long reaction times, tedious work-up procedures, co-occurrence of several side reactions, and poor selectivity.

Therefore, the search continues for a better catalyst for the synthesis of benzimidazoles in terms of; operational simplicity, economic viability, and in particular, with greater selectivity. 10

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