N-nitroso cyclamate

Hi USP exchange group,

We would like to ask for your support. Recently, we we looking at a nitroso assessment for an excipient that at least in EU is still accepted as sweetener in pharma Sodium cyclamate.

This excipient have a N-H bond and we expect a nitroso compound could be formed like N-nitroso cyclamate. What would be the acceptable intake in this case?

  • We are thinking of using Methylcyclohexylnitrosamine with an acceptable intake of 581 ng/day as surrogate



Currently, a nitrosamine must contain carbon chains at both sides of the Nitrogen, otherwise, it will fall out of the scope of CPCA categorization.

Reactivity wise, I would be surprised that the formation of the nitrosamine shown is straight-forward, since the sulfonic acid will reduce the reactivity of the Nitrogen due to its EWG nature


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Hi thanks for your comments!

You are right on the reactivity, also the pKa where the N-H bond is present is about 13.

Nonetheless, our evaluation relates to nitroso compounds, not nitrosamines. That is why we are suggesting directly a surrogate as CPCA is not applicable. Although, we are not sure if a nitrosamine could work as read across or we actually need a similar compound. Is our feeling that nitroso compound evaluations (not only nitrosamines) is starting to get more interest and better to start now.

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We should distinguish the other nitroso compounds from nitrosamines because they do not require metabolism for diazonium ion formation. The mechanism is different at all. The surrogate should be selected from non-nitrosamines. The following thread helps you understand the difference between nitrosamines and the other nitroso compounds.

HESI New (Q)SAR/QM Nitrosamines Working Group will start a discussion on the other nitrosamine compounds.

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Thanks a lot for your insights! We will then need to look for a proper surrogate.

In this part I have seen other forum members also with very valuable inputs in similar topics. May I ask to @ASrinivasan @David for their opinion too?

  • It is clear, no nitrosamine as surrogate for this compound. But what else? An Ames test?

Thanks a lot once again to all for the contribution.

Ames is a good place to start.

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I’d agree with @ASrinivasan on the Ames - there’s not really any other option. That said, my thought for all of these is that they are unlikely to have potency comparable to the cohort of concern as you can’t form a carbon-attached diazonium C-[N+]#N by hydroxylating the remaining carbon.

If this were a nitrosated hydroxylamine I’d strengthen from “unlikely” to go for the argument of non-CoC-potency from Ponting and Foster and jump straight for 1500, but the sulphonamide is different to any group we have carcinogenic potency data for so I suppose could theoretically (though unlikely) do other things… (not sure what - I’d need to sit down with some paper and push some curly arrows; if you do that and can’t find a reasonable route to a diazonium then, like the hydroxylamines, this argues against CoC).

If you do Ames test this, please share the results (here, privately, or get them published) - I would be very interested in the strain profile; which, if not TA100/TA1535 + S9, would argue for an alternate mechanism for mutagenicity and thus against it being likely to have CoC potency.

@Yosukemino mentions the HESI working group - we will indeed be looking at these in the future, so any experimental data would be valuable!


@David , I was thinking the same about the potency of these. I have worked with nitrosamines having tosylate, mesylate in beta position and they themselves did not have high TD50. Koeppky did some studies on that. I would also be interested in knowing about Ames. But I also want to remind you from the regulatory perspective that this is not a “nitrosamine”, so deadlines etc. are not applicable.


Thanks to all for the very insightful comments that give us more clarity on the topic.

We will look internally about a normal Ames test as well if it makes sense to use the Enhanced one with 30% S9, etc.

I recommend some further reading into sulfonyldiazohydroxide species and the stability of nitrosated cyclamate when designing an Ames test.