Isolation and structure determination of a novel spiro-gamma-lactam, spiro-arogenate

The eucaryotic microorganism, Neurospora crassa, is able under specified conditions (Zamir, L.O., Jung, E., and Jensen, R.A. (1982) J. Biol. Chem. 258, 6492-6496) to synthesize a cyclohexadienyl derivative of prephenic acid having the novel structure of a spiro-gamma-lactam. This L-gamma-(spiro-4-hydroxy-2,5-cyclohexadienyl)-pyroglutamate is herein given the trivial name, spiro-arogenate, to indicate its close relationship to the amino acid, L-arogenate. Spiro-arogenate is quantitatively converted to phenylalanine at mildly acidic pH and can be converted to arogenate by boiling at basic pH. The structure of spiro-arogenate was established through the application of spectroscopic techniques (ultraviolet, 1H-NMR, 13C-NMR, and mass spectrometry). The 1H-NMR and 13C-NMR spectra of spiro-arogenate isolated as the natural product conformed to the spectrum of spiro-arogenate prepared by chemical synthesis by S. Danishefsky and co-workers (Danishefsky, S., Morris, J., and Clizbe, L.A. (1981) J. Am. Chem. Soc. 103, 1602-1604). Circular dichroism established the S configuration of the asymmetric carbon at C-8 of spiro-arogenate.