Terpenoid chemistry. XXIV. (1R)-1-Methoxymyodesert-3-ene, an Iridoid Constitutent of Myoporum deserti (Myoporaceae)

Abstract

A common variety of Myopovum deserti A. Cunn. (Ellangowan Poison Bush) yields an essential oil consisting largely of the iridoid monoterpene, (1R)-1-methoxymyodesert-3-ene, C11Hls02, (1 R,4aS,7R,7aR)-1-methoxy-4,7-dimethyl-l,4a,5,6,7,7a-hexahydrocycopenta[c]pyran, b.p. 6772 mm, [@lo -165'. This cyclic acetal is hydrolysed to methanol and a mixture of two epimeric cyclopentanoid dialdehydes which are oxidized to the two epimeric trans,trans-nepetalinic acids and yield (+)-(R)actinidine with Brady's reagent. (1R)-1-Methoxymyodesert-3-ene is oxidized by ozone/hydrogen peroxide to (1R,2R,5R)-2-acetyl-5-methylcyclopentanecarboxylic acid.Hydrogenation yields mainly (1R)-methoxymyodesertan, hydrolysed by aqueous maleic acid at room temperature to methanol and a cyclic hemiacetal, (lR,4R,4aR,7R,7aR)-4,7-dimethyl-1,3,4,4a,5,6,7,7a-octahydrocyclopenta[c]pyran-1-01, Oxidation of this cis&-hemiacetal by bromine in acetate buffer yields a lactone further oxidized by chromic acid to (2R,1'S,2'R,3'R)-2-(2'-carboxy-3'-methylcyclopentyl)propionic acid.(1R)-1-Methoxymyodesertan, refluxed with aqueous phthalic acid, yields (+)-(4R,4aR,7R)-4,7-dimethyl-3,4,4a,5,6,7-hexahydrocyclopenta[c]pyran. Treatment of the hexahydropenta[c]pyran, the cis,cis-hemiacetal or (1R)-1-methoxymyodesertan with hydrochloric acid yields a tvans,transhemiacetal, (1 R,4R,4aR,7R,7aS)-4,7-dimethyl-1,3,4,4a,5,6,7,7a-octahydrocyclopenta[c]pyran-l-ol, which equilibrates in solution to a mixture of a-and j3-anomers. Spectral studies of these and other products establish the configuration of the natural product at C 1.(1R)-1-Methoxymyodesert-3-ene is not toxic to sheep as are the j3-substituted furans characteristic of most other chemovarieties of M. desevti.The shrub Myoporum deserti A. Cunn. (Ellangowan Poison Bush), which is found in the drier areas of Australia, is a well authenticated stock poison.' Previous parts2 of this series have described the isolation and chemistry of 11 toxic furanoid sesquiterpene ketones, such as (1) and (2), from various chemovarieties of the species but certain others contain iridoid monoterpenes accompanied by little or none of the toxic furanoid derivatives.

Stereoselective synthesis of trans-fused iridoid lactones and their identification in the parasitoid wasp Alloxysta victrix, Part I: Dihydronepetalactones

“…Analytical data of the first eluting component a were in accordance with those reported in the literature [ 24 ]. The same sequence starting from ( R )-pulegone yielded a mixture of diastereomers a' and b' .…”

“…Interestingly, the structure of a' is relatively close to that of nepetalactone 7 and lactol 8 , the sex pheromone of the grain aphid S. avenae [ 13 ] which keeps the second level in the investigated tetratrophic system. Grant et al, found the trans -fused (1 R ,4a S ,7 R ,7a R )-1-methoxy-4,7-dimethyl-1,4a,5,6,7,7a)-hexahydrocyclopenta[ c ]pyran, called (1 R )-1-methoxymyodesert-3-ene, among the volatiles of the Ellangowan poison bush, which they transformed to the corresponding lactone a' [ 24 ]. Apart from this compound and very few others, the stereogenic center carrying the methyl group in the five-membered ring of iridoid lactones including insect semiochemicals [ 13 – 15 ] generally shows ( S )-configuration.…”

The Diversity of Volatile Compounds in Australia’s Semi-Desert Genus Eremophila (Scrophulariaceae)

“…Several of the components were identified by isolation (10% ethyl acetate, 90% hexane, normal phase column chromatography using silica gel) and comparison of respective 13 C NMR spectra to published values, using a 500 MHz Bruker Avance (Germany) spectrometer in d-chloroform. These were: anymol [58], t-muurolol [59], freelingnite [60], ngaione [13], epingaione and dehydrongaione and dehydroepingaione [15], myoporone and dehydromyoporone [18], myodesmone and isomyodesmone [61], myomontanone [62], eremoacetal [63], methoxymyodesert-3ene [12], 1S-acetoxymyodesert-3-ene [16], myodesert-1-ene [3], mitchellenes G and B [4], 9-hydroxydendrolasin (listed as 6-hydroxydendrolasin in literature) [46], oppositifolic acid (as 5-acetoxymethyltetradeca-trans-2,trans-4,trans-6-trienoic acid) [48], germacrene-D-4-ol (listed as 1,6-germacradien-5-ol) [64], eremophilone and santalcamphor and 9-hydroxy-7(11),9-eremophiladien-8-one [7]. These components (Figure 9) were authenticated by matching 1 H or 13 C NMR spectra to published values (citations given in brackets).…”

“…Table 3 demonstrates the full chemical diversity of the species. By far the most common metabolite in leaves of E. deserti is methoxymyodesert-3-ene [12], which can vary in some specimens but is typically close to 100% of the gas chromatographic profile (the only component detected), which yields from the leaves at approximately 1-2% g/g of wet leaves. Furthermore, the cluster dendrogram of the chemistry of volatiles from the leaves of E. deserti conveys that the methoxymyodesert-3-ene type represents the most populated branch (Figure 2).…”

Stereoselective synthesis oftrans-fused iridoid lactones and their identification in the parasitoid waspAlloxysta victrix, Part II: Iridomyrmecins

“…Apart from very few exceptions such as methoxymyodesertene ( 24 ) [ 41 ], the 4- nor -nepetalactone mitsugashiwalactone ( 25 ) [ 42 ] and its “ nor -iridomyrmecin-complement” boschnialactone ( 26 ), [ 43 ] which all are plant volatiles, the methyl group in the typical five-membered ring of iridoids keeps its ( S )-configuration (see also Fig. 8 ), which is just in contrast to X and Z [ 44 ].…”