Nortaylorione a new nor-sesquiterpene, was identified among minor components of Artemisia annua (hybrid plants) essential oil. Its relative and absolute configurations were determined by GC and GC/MS equipped with a chiral column and coinjecting the essential oil with synthetic standards (racemic and homochiral), obtained in a few steps from commercial reagents. Pauson-Khand reaction was used as the key reaction in both synthetic pathways. The new natural product, named (+)-nortaylorione, is the (
Artemisia annua L is well known for its production of the antimalarial compound artemisinine 1.1 While adapting this asiatic plant to the Brazilian climate, a series of chemical analyses had to be performed in order to determine the chemical composition and ratio of its volatile and non volatile microconstituents. 2 In this process we have detected in the Artemisia annua 3 essential oil several minor constituents assigned as unknown oxygenated sesquiterpenes.
We were particularly intrigued by one compound (retention index=1746 (DB-5), 4 ca 0.02%) showing a molecular ion at m/z 220 and a base peak at m/z 43. Although the molecular ion was compatible with that of spathulenol 2 the mass spectra and the retention index were not. 5 The rather intense ion at m/z 436 was taken as a clue to the presence of a methyl ketone moiety. Several structures were suggested taking the relative retention index and the mass spectrum into consideration, nevertheless these evidences were too fragile to make any choice. Structure 5a, one of our preferred hypotheses, was based on the fact that the enzymatic system of Artemisia annua is rather aggressive in cleaving terpene double bonds as in artemisine 1 and in compound 3. Therefore formation of 5a could arise from an oxidative cleavage of a ledene derivative like 4 (Figure ). This hypothesis came up when a search in the literature revealed that taylorione 5b a sesquiterpene possessing an analogous skeleton was isolated from Mylia taylorii. 7
To isolate and characterize 5a, a large amount of essential oil would have to be available due to its low abundance. Unfortunately this was not the case and we were left with the alternative of synthesizing this compound.