Absolute Configuration of Chlorojanerin, a Chlorine-Containing Guaianolide from Centaurea scoparia

The title guaianolide, chlorojanerin [(1R, 3S, 4R, 5S, 6S, 7R, 8S)-4-chloromethyl-3,4-dihydroxy-8-(4-hydroxymethacryloyl)- 1H, 5H, 6H, 7H-guaia-10 (14),11 (13)-dien-6,12-olide,C₁₉H₂₃ClO₇], was obtained from the ethanol extracts of the air-dried aerial flowering parts of the Egyptian plant Centaurea scoparia Sieb. Its absolute configuration has been elucidated by X-ray analysis, which confirms the structure as a chlorine-containing guaianolide with the 4-hydroxymethacryloyl function at the C8 position, as previously proposed on the basis of ¹H NMR and CD spectral evidence.

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