Kaurane

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Kaurane is a parent hydride used in the IUPAC nomenclature of natural products and also, distinctly, in CAS nomenclature. It is a diterpene with a rigid four-ring structure and six chiral centres.

The stereochemistry of the six chiral centres is defined by convention: however, IUPAC and CAS use different conventional stereochemistry, which also leads to a slight difference in numbering between the two systems. IUPAC conventional kaurane has (5S,8S,9S,10S,13S,15R)-stereochemistry, and is drawn with the five-membered ring receding into the plane of the image.[1] CAS conventional kaurane has (5S,8R,9S,10S,13R,15R)-stereochemistry, and is drawn with the five-membered ring protruding from the plane of the image.[2] Carbon-19 (one of the two methyl groups attached to carbon-4) is on the same side of the molecule as the five-membered ring in both systems: hence it is receding into the plane of the image in IUPAC nomenclature and protruding from the plane of the image in CAS nomenclature.

The name ent-kaurane is sometimes used to refer to the CAS conventional kaurane and so to distinguish it from the IUPAC stereochemistry. It is also possible to explicitly specify the stereochemistry at carbons 8 and 13, giving:

  • (8S,13S)-kaurane (IUPAC conventional)
  • (8R,13R)-kaurane (CAS conventional)

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Further reading

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