Thursday, October 15, 2009

Hopane, a pentacyclic triterpane named—indirectly—after English botanist John Hope

Hopane and its derivatives (hopanoids) are chemical compounds that occur in certain tropical plants and also in bacterial cell membranes. Further, they have been found in rock and sediment layers that formed in inland lakes and seas, recently—on a paleontological time scale—or during the Eocene. For example, hopanes were identified in samples from Messel and Green River shales.

Hopane got its name from a Burmese tree, the Hopea tree, which was named after the British botanist John Hope [1]:
[…] a 30-carbon five-ring affair that people had taken to calling the “hopane” skeleton—not because it inspired particularly positive expectations, but because the genus of Burmese trees where it was first discovered was named after an eighteenth-century English botanist named John Hope. Probably the only reason anyone knew about hopane to begin with was that the British Museum has used resin from Hopea trees as a varnish. What was disconcerting was that compounds with this hopane ring structure were present in every rock or sediment sample one analyzed, no matter when or where it was formed. And yet, as far as anyone knew, such compounds were made only by a few exotic species of tropical trees, ferns, and mosses.
The question that remains is Does this Burmese tree species or genus not have a Burmese (Myanmar) name? And if yes, shouldn't the name hopane change into a more Burmese-flavored name? A nightmare for chemical nomenclature!
Anyway, this wouldn't change the molecular structure of hopane (C30H52), a hydrocarbon molecule, which is shown in the sketch above with its carbon numbering and ring lettering.

Keywords: organic chemistry, botany, tree resin, history

[1] Susan M. Gaines, Geoffrey Eglington, and Jürgen Rullkötter: Echoes of LifeWhat Fossil Molecules Reveal about Earth History. Oxford University Press, New York, 2009; page 62.

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