The Structures of Two Alkaloids from Patchouli Oil

Preparative isolation of guaipyridine sesquiterpene alkaloid from Artemisia rupestris L. flowers using high‐speed counter‐current chromatography

“…The UV absorption maxima at 219 (sh), 271 and 275 nm were characteristic of a typical guaipyridine alkaloid [10,11]. Two pyridine protons appeared as a typical AB pattern (J = 8.4 Hz) at d 7.50 and 8.11 ppm (H-39, and H-49) [10] in the 1 H NMR spectrum.…”

“…The UV absorption maxima at 219 (sh), 271 and 275 nm were characteristic of a typical guaipyridine alkaloid [10,11]. Two pyridine protons appeared as a typical AB pattern (J = 8.4 Hz) at d 7.50 and 8.11 ppm (H-39, and H-49) [10] in the 1 H NMR spectrum. Two single signals at d 5.68 and 6.19 ppm (H-3a, and H3b) belonged to vinylic hydrogens of a,b-unsaturated carboxylic acid with signal of d 170.6 ppm (C-1) [3], which is different from isopropylene group of epiguaipyridine [10].…”

“…To the best of our knowledge, the first guaipyridine sesquiterpene alkaloid in nature was found in pachouli oil in terms of epiguaipyrine in 1966 [10]. Over the past 40 years, this type of compounds has never been isolated in nature again except for cananodine which was isolated from the fruits of Cananga odorata [11].…”

The Chemistry of the Sesquiterpene Alkaloids

“…18 The other guaipyridines that have been isolated are also shown in the same Figure 5 for comparison.…”

“…The original Büchi laboratory publication of the two alkaloids ( Figure 5) also introduced a synthesis of patchoulipyridine from β-patchoulene by reaction with hydrazoic acid (Scheme 9). 18 The initial addition product with HN 3 rearranges as indicated, and is then dehydrogenated (aromatised) to a mixture including patchoulipyridine as the major product, after chromatographic separation. The addition of HN 3 to β-patchoulene is not regioselective, and the other possible addition leads to a minor isomeric pyridine product, as shown in Scheme 9.…”