"Acyclovir Impurity B" is the name for guanine used by a handful of websites. Googling the term shows this.

https://www.trc-canada.com/product-detail/?G836000 which seems to confirm that that "acyclovir impurity B" really is another name for guanine, albeit very rarely used.

https://acanthusresearch.com/synonyms/2-amino-19-dihydro-6h-purin-6-one/ is another website that does this.

There's nothing to indicate that guanine is ever referred by this name in Wikipedia.The closest I could find in Wikipedia by Googling "acyclovir impurity B" was this page: https://en.wikipedia.org/wiki/Aciclovir which contains "The aciclovir metabolite 9-Carboxymethoxymethylguanine (9-CMMG) has been shown to play a role in neurological adverse events, particularly in older people and those with reduced renal function.[34][35][36]" which contains the string "guanine".

It looks like many to all sites using the term "acyclovir impurity B" are selling it.

  • 1
    $\begingroup$ This paper says it is the main impurity found in samples of the drug acyclovir. When you test for impurities, you need standards to identify and quantify compounds present in the sample. For shopper's convenience, you might want to mention the drug that is undergoing quality control. In all other contexts, this might not be relevant. $\endgroup$
    – Karsten Mod
    Dec 19, 2022 at 22:09
  • 3
    $\begingroup$ You have a question, and it seems like you did some research. I would not close this as off-topic on the main site, but I can't speak for the other thousand or so folks with closing vote privileges. I would post it if I were interested in the answer. $\endgroup$
    – Karsten Mod
    Dec 19, 2022 at 22:12
  • 2
    $\begingroup$ I also think that the question should be on topic. I don't think it'll do bad either. I recommend giving it a try. $\endgroup$ Dec 19, 2022 at 23:57
  • $\begingroup$ Yes, such questions are allowed. See: chemistry.stackexchange.com/questions/62590/… where OP challenged the drug name vs brand name $\endgroup$ Dec 20, 2022 at 4:00
  • $\begingroup$ It's definitely chemistry (so on topic) but I am not sure you might not be looking at this backwards so I'm a bit curious to know more about your reasoning. The structure of acyclovir includes a guanine moiety. Even if guanine is not a starting compound it might be generated as "acyclovir impurity B" during synthesis. $\endgroup$
    – Buck Thorn Mod
    Dec 20, 2022 at 15:51
  • $\begingroup$ It is interesting that the synonym "acyclovir impurity B" should be provided on sites selling guanine. I would think that if someone is interested in guanine it might catch their eye as they might not be familiar with this application of guanine as part of the guanosine analog acyclovir. But anyone studying acyclovir would probably be very familiar with guanine. $\endgroup$
    – Buck Thorn Mod
    Dec 20, 2022 at 15:56


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