Probability Breakdown

The article "Hand over Hand" (C&EN, March 23, page 38) prompts us to make readers aware of work on Cylert (pemoline) carried out at Abbott Laboratories and presented in 1999 ("Spontaneous resolution and interconversion of enantiomers in 2-imino-5-phenyl-4-oxazolidinone [pemoline]," Book of Abstracts. Bonk, Peter J., et al. 22-26, 1999, ORGN-538).

We made up a relatively large batch of pemoline, and after the reaction was essentially complete as determined by high-performance liquid chromatography, and prior to the start of crystallization, the large batch was split into six separate flasks. After crystallization, each flask yielded a significantly different enantiomeric ratio, some with an excess of the (+) enantiomer and some with an excess of the (-) enantiomer.

The criteria for the behavior we observed were delineated 55 years ago by Egbert Havinga (Biochim. Biophys. Acta 1954, 13, 171), who included examples he uncovered over several years of observation in the 1940s. At the core of the phenomena is a surprising breakdown of the "expected" 50:50 ratio of nucleation of the separate (R) and (S) crystals that make up the conglomerate solid. The initial imbalance to one enantiomer occurs only during the nucleation/crystallization process; the liquors are always spot-on racemic.

Although not explicitly discussed in our poster, the implications to "life's single chirality" are obvious. I recently presented the data in a seminar at both Clemson University and Florida Institute of Technology. A manuscript to be submitted to Organic Process Research & Development is in final preparation and will make our observations, data, and results more readily accessible.

Peter J. Bonk
Westerly, R.I.