Wednesday, July 4, 2012

Head-Scratching "Sanros" Structures

It's like a crossword puzzle...
Source: Chemistry World
Over at Chemistry World, Duncan Browne posted a review of a new applet version of the Kurti / Czako book Strategic Applications of Named Reactions in Organic Synthesis (for the hip iPhone crowd, the title has been condensed to simply "Sanros"). The trial version allows access to 25 out of the 250 reactions included in paid access. I'm all for chemistry-enabled free software making its way out into the public.

Just one tiny problem: what the heck is that structure? Maybe the atoms were inadverently deleted in transit, or perhaps it's meant as an artistic statement? I can't imagine this molecular graphic falls under Elsevier copyright protection.

In a way, it's like a detective mystery: can you infer what's missing? I took a crack at it myself (see below). I figured the structure on the right was either a dithiane (S,S) or ketal (O,O). The bottom ring could have any combination of N,O,S, so we'll swap in a morpholine. The aromatic? Gotta be a pyridine. Uh-oh, there could be anything terminating those 'short' bonds on the cyclopentane, or on the alpha bonds stemming below the cyclopropane. I'll just infer methyl groups, for now.


Of course, without knowing the actual natural product, and without access to database software due to the holiday, I have no way to know if I'm barking up the right tree. Anyone care to help?


Happy Fourth of July, everyone!


Update, 7/4/12 - Commenter @azmanam wins the platinum coin for his search efforts, locating the correct intermediate from a Boger total synthesis (see below). So, in the end, I went 4 for 9 on "mystery atoms!"

10 comments:

  1. Nothing shows up in Scifinder when all of the blanks are set to "any atom except H," or deleted. My money is on made up artistic looking structure.

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  2. Boo. With all the gorgeous natural products in the world, they don't have one on the front? Maybe it's a drug lead, buried in the patent lit...sometimes SciFinder won't catch the Markush very well.

    Thanks!

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  3. Winnar!

    Intermediate in Boger's synthesis of rubrolone aglycone

    (cpd #18: http://dx.doi.org/10.1021/ja002997b) Neat little D-A reaction to form the intermediate :)

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    1. Can I post images? If yes, the real structure will be shown below.

      [img]http://i.imgur.com/U00e4.png[/img]

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  4. Bah, I had assumed methyl groups, not -H and -OMe.

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  5. Note the ghostly structure is also missing the gem-dimethyl on the ketal, too.

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    Replies
    1. So, you're saying, artistic or not, it seems to be a hack job.

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  6. The complete structure (when viewed at an angle) is remarkably anthropomorphic.

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  7. From the Publisher: Congratulations on solving this puzzle. As you have correctly identified, the artistic fragment was produced by deleting heteroatoms from an intermediate in Dale Boger’s synthesis of rubrolone aglycon; one of 4 examples of the Diels-Alder reaction provided in the book and app (www.namedreactions.com).

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    Replies
    1. Hooray! This means we all win free copies....right? : )

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