No abstract

The true aglycones of the avenacins are acid sensitive triterpene 12,13-epoxides, not 1 2-ketonesr and one such avenestergenin epoxide is isolated direct from oat roots; this, together with study of the attached trisaccharide, permits complete structures t o be proposed for the four avenacins (3a-d); avenestergenins readily undergo an a c i d -ca t a I y sed a n h y d rod i m e r i sat i o n via acet a I f o r m at i o n .

Syntheses of a series of compounds which merge a m-dihydroxybibenzyl with a terpenoid structure, giving a series of hybrid cannabinoids in which products of two major biogenetic routes of Cannabis are united, are described. The compounds made are the bibenzyllo-and p-cannabigerols ( 1 9) and (1 8 ) / 0and p-cannabidiols ( 21) and ( 20),/A'-THC ( 22),/A6-THC ( 23),/0-and p-cannabichromenes (25) and (24),/0and p-cannabicyclols (28) and ( 27) and/cannabicitran (26). Chromatographic and spectral data are listed in order t o facilitate search for such 'crossed' types since only the bibenzyl cannabigerols and a chromene have as yet been found in natural sources.The bibenzyllp-cannabigerol ( 1 8 ) has been reported in Helichrysum umbraculigerum (Compositae) and the liverwort Radula variabilis. Our synthetic work confirms the former observation, but the liverwort compound appears to be its o-isomer.The so-called cannabinoid class of natural products found in Cannabis suctira is generally considered to be a biogenetically related group, though actual experimental information is sparse.' Scheme 1 shows the core of the relationships, dealing * Unaware of our earlier work, these compounds have very recently been rediscovered and named canniflavins-h and -B.&

ChemInform Abstract Catalyzed by TosOH, (R)-(-)-α-phellandrene (I) reacts with olivetol (II) to give the dihydro-p-and -o-cannabidiols (III) and (IV). At 80 rc C under the acid conditions the latter retrogresses to the former and both cyclize to give the p-isotetrahydrocannabinol (V) with 51% yield and only 3% of the corresponding o-isomer. Terpenylation of the dihydrochalcone (VI) yields the natural meroterpene linderatin (VII).

Examination of the toluene-p-sulphonic acid-catalysed reaction of (1 S,2S,3R,6R) -(+) -trans-car-Zene epoxide with olivetol shows that, inconsistently with the accepted mechanism, (3R,4R) -(-) -0 -and -pcannabidiols are produced as well as (3R,4R) -(-) -A1-and A6-tetrahydrocannabinols. Evidence is n o w presented that, as in Petrzilka's reaction employing chiral p-mentha-2,8-dien-1 -ols, the reacting species is the delocalised (4R)-p-mentha-2,8-dien-l -yl cation (9).Similar terpenylation using (1 S,3S,4R,6R) -(+) -trans-car-3-ene epoxide shows that besides the reported (-)-A6-THC, 0 -and p-cannabidiols, A'-THC and A4**-iso-THC can also be produced. The nature of the products, the chirality, and the characteristics of the reaction implicate again the delocalised cation (9). Its formation via Kropp-type rearrangement is excluded and a pathway leading to (4R)-pmentha-2,6,8-triene, which on protonation gives (9), is proposed. Protonated on C-8, the triene can be trapped and isolated as (4R) -p-mentha-2,6-dien-8-01. The latter, made in ( & )-form from citral, proved to be an excellent terpenylating agent for producing cannabinoids.* The prefixes orrho-and para-are used with reference to the C,-olivetol side chain. The former series are sometimes referred to as 'abnormal' and prefixed abn.