Pyridine monoterpene alkaloid formation from iridoid glycosides. A novel PMTA dimer from geniposide.
New pyridine monoterpene alkaloids (PMTAs) have been synthesized from the iridoid glycosides 8-epi-loganin, cornin, and antirrinoside by treatment with beta-glucosidase and aqueous NH4-OAc. The PMTA from antirrinoside contained an 8-alpha-OAc group from the opened 7,8-epoxide moiety. Treatment of genipin, the aglycone of geniposide, with HCl(g) and NH3(g) yielded the PMTA racemigerine, a known plant isolate, in which the C=C-CH2OH side chain was converted to C=C-CH3. Reaction of geniposide with beta-glucosidase and aqueous NH4OAc led to oligomeric alkaloids, but at high dilution a dimer was obtained whose structure was formally that of a Diels-Alder adduct between racemigerine and a dihydropyridine. These biomimetic semisyntheses were analyzed in terms of reaction mechanisms and the relative paucity of known plant PMTAs in comparison with the multitudinous occurrence of their presumed iridoid glycoside precursors.
Frederiksen
S M
SM
Department of Chemistry, Colorado State University, Fort Collins 80523-1872, USA.
Stermitz
F R
FR
D006027:Glycosides / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D010946:Plants, Medicinal / Q000737:chemistry; D011725:Pyridines / Q000737:chemistry*; D016339:Spectrometry, Mass, Fast Atom Bombardment; D014961:X-Ray Diffraction
D006027:Glycosides; D011725:Pyridines