Is ethano a bridge too far?

Issue #31 resolved
Steve Chapman
created an issue

Comments (5)

  1. Daniel Lowe repo owner

    OPSIN in this case is enforcing the IUPAC rule that bridges are supposed to be "non-detachable" prefixes hence it will handle the case where the bridge is adjacent to the morphinan: (2S)-2-[(5R,6R,7R,14S)-N-cyclopropylmethyl-4,5-epoxy-3-hydroxy-6-methoxy-6,14-ethanomorphinan-7-yl]-3,3-dimethylpentan-2-ol

    which possibly should be this if the epoxy is also considered to be a non-detachable bridge: (2S)-2-[(5R,6R,7R,14S)-N-cyclopropylmethyl-3-hydroxy-6-methoxy-4,5-epoxy-6,14-ethanomorphinan-7-yl]-3,3-dimethylpentan-2-ol

    I think whether epoxy is considered detachable or non-detachable may actually depend on the version of the IUPAC guidelines you look at. In http://www.acdlabs.com/iupac/nomenclature/79/r79_879.htm it seems to have been listed in both categories! (the current recommendations seem to have it as non-detachable... unless applied to a carotenoid!)

    Anyway the name you gave is completely unambiguous so I think it would make more sense to allow this slight deviation from the recommendations and handle alkane bridges analogous to how epoxy is handled i.e. allow it to be detachable or non-detachable.

  2. Steve Chapman reporter

    Thanks Daniel, I wasn't aware of the detachable/non-detachable rules for bridges. The name was taken from a recent journal article.

    I agree that so long as there's no ambiguity it would be handy if this kind of construction was allowed for. It may take some time before that rule is widely understood and followed.

  3. Daniel Lowe repo owner

    This is now fixed, I'll update the web service at some point. The rewrite to fix this had the nice side effect of fixing a bug I was not even aware of where epimino bridges were not being assigned a locant.

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