Wednesday, September 26, 2007

Cyanation of aryl halides

There are several methods available for the cyanation of aryl halides. However a common problem with many of the more traditional methods is that they are very toxic# One method to full fill these criteria has been around for a while (Weissman S A et al, J. Org. Chem.2005, 70, 1508-1510.) Ligand- free, Palladium- catalyzed cyanation of aryl halides.Potassium hexacyanoferrate(II) has used as cyanide source. This result increase the list of metal catalyzed reactions that can be performed without ligand.

The advantage of this method is obvious, in contrast to other cyanating agents potassium hexacyanoferrate(II) is less poisonous# and can be handle without special precaution, due to the slow release of cyanide ions a significantly improved the catalytic productivity compared to previously know procedures in achieved.

#( KCN is extremely toxic (LDL0(oral, human) =2.86mg Kg-1 and develop HCN on contract with acidic water. K4[Fe(CN)6]­ is non toxic and used in food industry for metal precipitation in wine. Also it has been used as anti agglutinating auxiliary for NaCl (table salt). It is soluble in water without decomposition. Schareina T et al, Chem Commun., 2004, 1388-1389.)

Saturday, September 8, 2007

Myers Asymmetric Alkylation

Psuedoephedrine is a chiral auxiliary used for the synthesis of enantiomerically enriched carboxylic acid, aldehyde, alcohol and ketones.
Both enantiomers of pseudoephedrine are inexpensive and can be N-acylated in high yields to form tertiary amides. In the presence of lithium chloride, the enolates of the corresponding pseudoephedrine amides undergo highly diastereoselective alkylations with a wide range of alkyl halides.


Advantages of using psuedoephedrine as chiral auxiliary,

• Enolate of pseudoephedrine amide undergo efficient and high diastreoselective alkylation with wide variety of alkyl halides.
• High enantiometrically enriched carboxylic acids, alcohols, aldehydes and ketones
• Large scale/ Preocess application ( low cost of auxiliary, crystallinity of starting materials and products, no carcinogenic solvents.)
Ref.: Myers, A.G. et al., J. Am. Chem. Soc., 1997, 119 , 6496

Friday, September 7, 2007

Racemic Switch

A "racemic switch" is the redevelopment in single-enantiomer form of a drug that was first approved as a racemate. Sometimes, the pharmaceutical activity is in only one enantiomer and the other is inactive, or the "other" enantiomer has a different kind of activity from the first.

Omeprazole

Omeprazole is a Antiulcer drug (AstraZeneca) .It was marketed in U.S. as a racemic drug in 1995. The patent ran out in 2002. Since pharmacological property lies in (S)-enantiomer, the company has patented now (S)-enantiomer.