Is there any possibility of formation of N-nitroso dabrafenib in the dabrafenib API?
Dear Bruno,
according to my opinion it is very difficult the formation of this nitrosamine.
The targeted nitrogen is next to an aromatic ring and to a sulfonamide group which means that is a very weak nucleophile to react with a nitrosonium ion.
I would recommend you to try to order it from two or three vendors with a commitment to provide you a justification letter in case of failure.
Christos
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And no alpha-hydrogen either …
Are we in the presence of another impossible to synthesized impurity that supplier are selling? 
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Probability of nitroso formation looks low. Experimental data will be required to support this observation.