1. Could anyone share where I can obtain or purchase the reference standard for N-Nitroso N-Desmethyl Rosuvastatin?
2. I was told that synthesizing N-Nitroso N-Desmethyl Rosuvastatin is difficult and the request was declined. Does anyone know why the synthesis process is considered challenging? Please share any insights.
i can find some suppliers eg Synzeal and Veerpho.
Veerpho also provides failure report in case synthesis is not possible. there is a related discussion here Synthesis Attempts and Failure Report 
- Confirmatory Testing & Analytical Challenges - Nitrosamines Exchange
Dear Jueun,
regarding the N-Desmethyl Rosuvastatin, its activity as nitrosated molecule would be very low as its negative charge of the nitrogen would be extensively delocalized through the resonance with the aromatic ring and the sulfonyl group.
So, the possibility of the formation of the N-Nitroso N-Desmethyl Rosuvastatin would very low or even negligible.
Overall, given the fact that the formation (even theoritical) of the N-Nitroso N-Desmethyl Rosuvastatin requires demethylation and then nitrosation of a non-vulnerable amine, i would not consider as a risk this ‘‘nitrosamine’’.
thanks
Christos
As explained by Chrischar, environment of secondary nitrogen plays big role in nitrosamine formation reactions. I will also review and look for any source if available in india. You can please write to me for any requirements of nitrosamine impurites/NDSRIs @ kamal@riverxlab.com
Thank you for your response. I have contacted the following suppliers — SYNTHINK, SIMSON, VEEPHRO, CHEMICEA, ALLMPUS, SYNZEAL, MOLCAN, CLEARSYNTH, and PHARMAFFLITES — but the purchase could not be completed due to lack of stock and inability to synthesize the material.
Dear Christos,
May I get any supportive reference for N-Desmethyl Rosuvastatin.
Thank you,
Ellen
Dear Ellen,
apparently this reference is not feasible to be synthesized, at least with convential nitrosation reactions.
My suggestion is to looking for a failure report regarding its synthesis. As it has been told from Eleni above, Veeprho could provide something like this. I am sure that several other companies could also provide something similar.
best regards
Christos
The core nitrogen atom on this impurity belongs to a sulfonamide functionality, not an amine; since the adjacent sulfonyl group is highly electron-withdrawing, it drastically reduces the nitrogen’s electron density and nucleophilicity, making standard or dealkylative nitrosation chemically remote.
This theoretical limitation is conclusively supported by the fact that none of the commercial impurity suppliers are able to supply the impurity. From our experience too, the synthesis attempts were unsuccessful. Furthermore, the molecule is completely absent from all regulatory guidance appendices, confirming it is not a recognized risk for this drug class.
I agree with all you are saying but the last bit. A molecule being absent from nitrosamine listings is not proof at all that there is no recognized risk. Those lists are far from extensive
Dear Javier,
I agree with you on this. As mentioned this is not the only factor considered. Chemistry, unavailability in market, synthesis failures were also considered.
Well noted and thank you very much for your information.
Well noted with thanks. 
