September 10, 2012
Image of Bosutinib 3D Image of Bosutinib

Bosutinib is a tyrosine kinase inhibitor being developed by Pfizer to treat chronic myeloid leukemia. During the Phase III trials, an unusual problem occurred. N. M. Levinson at Stanford University noticed that a databank structure of bosutinib bound to a kinase was inconsistent with authentic bosutinib. It turned out that a methoxy group and two chlorine atoms on the molecule’s aniline substituent were in the wrong positions (see lower inset). An investigation showed that the “wrong” isomer has been used in many medical trials since 2006.

MOTW Update

Herbicides glyphosate and 2,4-dichlorophenoxyacetic acid were Molecules of the Week on October 5, 2009, and August 12, 2012, respectively. In October 2014, the US Environmental Protection Agency (EPA) awarded a registration to Dow AgroSciences for Enlist Duo, a combination of these chemicals. But last month the EPA asked a federal court to rescind its approval on the basis that Dow may have understated its toxicity to nontarget plants. Dow believes that EPA’s concerns can be overcome before the start of the 2016 growing season.

The September 9, 2012, molecule was the kinase inhibitor bosutinib. It was notorious at the time because researchers were unwittingly performing studies on a compound labeled as bosutinib, which was in fact one of its isomers. Now Pfizer chemists have developed simple analytical methods that distinguish the drug from its isomers.

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