W. Mary L. Crombie

Pathogenicity of ‘take-all’ fungus to oats: Its relationship to the concentration and detoxification of the four avenacins

Abstract Data for inhibition of the growth of Gaeumannomyces graminis var. tritici (Ggt) and var. avenae (Gga), Phialophora radicicola and Fusarium avenaceum , caused by avenacins, are presented. The avenacins found in all oat species examined are sufficient in quantity to totally suppress growth of wheat ‘take-all’ (Ggt), even old roots containing 25 μg/g (fr. wt). Fungal variants that can also attack oats [var. avenae (Gga)] show considerable variations in their tolerance to avenacin A-1, ec 50 values being 5–80 μg/ml. Nevertheless, all Gga isolates maintained some growth at avenacin A-1 concentrations as high as 200 μg/ml and it is this ability to grow, albeit slowly, at high concentrations that is the critical difference between Gga and Ggt strains. The pathogenicity towards oats of a range of isolates of Gga is related to the fungicidal activity of avenacins. Gga pathogenicity is shown to increase with poor nutrition of the oat hosts (poor illumination, lack of minerals). Fungal detoxification of avenacins produces mono-deglucosylavenacin A-1, bis-deglucosylavenacin A-1 and, in one case, tris-deglycosylavenacin A-1. Ggt strains left avenacin A-1 almost unaffected giving only traces of mono-deglucosyl product. Gga strains bring about mono- and bis-deglucosylation whilst Fusarium avenaceum causes mainly bis-deglucosylation. Mono-deglucosylavenacin is shown to be less inhibitory to Gga than is avenacin A-1, whilst the bis-deglucosyl compound is still less inhibitory.

Natural products of Thailand high Δ1-THC-strain Cannabis. The bibenzyl-spiran-dihydrophenanthrene group: relations with cannabinoids and canniflavones

Since non-cannabinoids may influence the pharmacological profile of Cannabis-leaf drug, a detailed examination of the acidic fraction from leaf extractive has been made. Twelve non-cannabinoids have been isolated crystalline from a single high Δ1-THC-strain of Thailand Cannabis grown in Nottingham under controlled conditions: nine of the compounds were not previously known as natural products and their structures have been determined. The extractives comprise three bibenzyls, six spirans, two 9,10-dihydrophenanthrenes, and two prenylated flavones.The bibenzyls, spirans, and dihydrophenanthrenes may be linked together in a biogenetic scheme in which one-electron oxidation and reductive processes play important parts: the scheme is particularly supported by the discovery of a new spiran, cannabispiradienone, which holds a key position and undergoes a dienone–phenol rearrangement to give one of the new dihydrophenanthrenes. Relations between bibenzyl, cannabinoid, and flavone pathways are briefly considered.

Structures of the oat root resistance factors to ‘take-all’ disease, avenancins A-1, A-2, B-1 and B-2 and their companion substances

It is shown that avenestergenins, having a 12-oxo group, are not true aglycones of the avenacin series: the latter are 12, 13β-epoxides. Acid hydrolysis would be expected to lead to a 13α, 12-ketone, not the 13β, 12-ketone of the avenestergenins, and the chemistry of the process is modelled using the 12α, 13α- and 12β, 13β-epoxides from 3β-benzoyloxyolean-12-ene and isolating the 13α, and 13β, 12-ketones. The former is readily converted into the latter under acid conditions similar to those employed for hydrolysis of the avenacins. Search of the oat extractives has resulted in isolation of the true free aglycone of the avenacin A-1 series, named epoxyavenagenin A-1.By combination of f.a.b. m.s., methylation, 13C and 1H n.m.r. techniques, the trisaccharide chain of all four avenacines is shown to be [β-D-glucopyranosyl(1 → 4)]-[β-D-glucopyranosyl(1 → 2)]-α-L-arabinopyranosyl attached at the triterpene 3-β-hydroxy group. This completes structural and stereochemical details for avenacins A-1, A-2, B-1, and B-2.As minor components of healthy oat root extract, two compounds formulated as glucoavenacin A-1 and deglucoavenacin A-1 have been isolated. The latter is of particular interest as, along with bis-deglucoavenacin A-1, they are detoxified products of avenacin A-1 formed by the highly virulent Gaeumannomyces graminis var. avena which can attack oat roots.

Structures of the four avenacins, oat root resistance factors to ‘take-all’ disease

The true aglycones of the avenacins are acid sensitive triterpene 12,13-epoxides, not 12-ketones, and one such avenestergenin epoxide is isolated direct from oat roots; this, together with study of the attached trisaccharide, permits complete structures to be proposed for the four avenacins (3a—d); avenestergenins readily undergo an acid-catalysed anhydrodimerisation via acetal formation.

Cannabinoid formation in Cannabis sativa grafted inter-racially, and with two Humulus species

Abstract Inter-racial grafts between high and low Δ 1 -THC strains of Cannabis sativa , as well as cross-grafts with two Humulus (hop) species have been effected. C. sativa strains continue to produce essentially their own characteristic mixtures of cannabinoids, with undiminished vigour, whatever part of the graft system they form. There is no evidence of transport of intermediates or factors critical to cannabinoid formation across the grafts.

Synthesis of bibenzyl cannabinoids, hybrids of two biogenetic series found in Cannabis sativa

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 bibenzyl/o- and p-cannabigerols (19) and (18)/o- and p-cannabidiols (21) and (20),/Δ1-THC (22),/Δ6-THC (23),/o- and p-cannabichromenes (25) and (24),/o- and p-cannabicyclols (28) and (27) and/cannabicitran (26). Chromatographic and spectral data are listed in order to facilitate search for such ‘crossed’ types since only the bibenzyl cannabigerols and a chromene have as yet been found in natural sources.The bibenzyl/p-cannabigerol (18) 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.

Isolation of avenacins A–1, A–2, B–1, and B–2 from oat roots: structures of their ‘aglycones’, the avenestergenins

Four antifungal avenacins are isolated from oat roots: the structures of their ‘aglycones’, avenestergenins A–1, A–2, B–1, and B–2, are shown to be N-methylanthranilic or benzoic esters of an unusually oxygenated oleanane triterpene.

Rotenoids of Lonchocarpus salvadorensis: their effectiveness in protecting seeds against bruchid predation

Abstract Seeds of the legume Lonchocarpus salvadorensis , having unusually low bruchid predation, contain deguelin (0.29%) rotenone (0.22%), elliptone (0.06%) and α-toxicarol (0.003%). The relation between rotenone content and toxicity towards the generalist bruchid Callosobruchus maculatus is examined and quantified.

Acid-catalysed terpenylations of olivetol in the synthesis of cannabinoids

Examination of the toluene-p-sulphonic acid-catalysed reaction of (1S,2S,3R,6R)-(+)-trans-car-2-ene epoxide with olivetol shows that, inconsistently with the accepted mechanism, (3R,4R)-(–)-o- and -p-cannabidiols are produced as well as (3R,4R)-(–)-Δ1-and Δ6-tetrahydrocannabinols. Evidence is now presented that, as in Petrzilkas reaction employing chiral p-mentha-2,8-dien-1-ols, the reacting species is the delocalised (4R)-p-mentha-2,8-dien-1-yl cation (9).Similar terpenylation using (1S,3S,4R,6R)-(+)-trans-car-3-ene epoxide shows that besides the reported (–)-Δ6-THC, o- and p-cannabidiols, Δ1-THC and Δ4,8-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)-p-mentha-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-ol. The latter, made in (±)-form from citral, proved to be an excellent terpenylating agent for producing cannabinoids.Terpenylation of olivetol by the pinanes (1S,4S,5S)-(–)-cis-verbenol and (1R,5S,7R)-(+)-cis-chrysanthenol is compared. A major drawback of the latter is partial racemisation which occurs in the verbenone–chrysanthenone isomerisation during its photochemical preparation. Whilst Δ1-THC cannot be directly obtained from verbenol, its tertiary allylic cation permits a much higher yielding terpenylation than the secondary cation from chrysanthenol.

Germacranolides of Erlangea cordifolia: structure and absolute stereochemistry of cordifene and cordifene 4β,15-oxide by X-ray and spectrosopic methods

Cordifene and cordifene 4β,15-oxide, extracted from the insect-antifeedant plant Erlangea cordifolia, have been examined by spectroscopic and X-ray techniques. Cordifene is shown by X-ray analysis (R 5.49%) as its 5-bromo-2-furoate (3c) to be the 8-angelate ester of a 1R,2S,3S,5S,6S,7R,8S,10R-6,7-lactonised dihydroxygermacranolide bis-epoxide (3a). Cordifene 4β,15-oxide, having three contiguous epoxide groups and nine chiral centres, is the 4R-derivative (2a), as demonstrated by direct X-ray methods (R 3.2%): its abolute configuration is linked to (3a) by c.d. methods. On the basis of Stocklins rules, the signature of the n→π* c.d. maximum leads to an incorrect absolute configuration for both compounds, but the Beecham–McPhail treatment satisfactorily explains the situation. 1H N.m.r. data indicate that solution conformations are similar to crystal conformations.