NMR assignments and absolute stereochemistry of two guaianolide sesquiterpenes from Tanacetum densume subsp. amani

Abstract

The guaianolide sesquiterpene pyrethroidinin (1) and the corresponding ketone parishin A (2) were isolated from Tunacetum densum subsp. amuni (Asteraceae). The absolute stereochemistry of 1 was established as (lR, 3R, 6S, 7S, 10R) on the basis of the differential shielding in the 'H NMR spectra of the (-)-and (+)-0-methylmandelate esters. The structure, including absolute stereochemistry, of 2 was confirmed by oxidation of 1 with Jones' reagent.

Essential Oil Composition and Antibacterial Activity of Tanacetum argenteum (Lam.) Willd. ssp. argenteum and T. densum (Lab.) Schultz Bip. ssp. amani Heywood from Turkey

“…Tanacetum densum is represented with four subspecies all are endemic in Turkey. Previous investigations on this species include essential oil composition 8,9 and chemistry [10][11][12][13][14][15] of ssp. amani, ssp.…”

Preparation and Phytotoxicity Evaluation of 11,13-Dehydro seco-Guaianolides

“…Parishin A (14) 23,24 was obtained by a photochemical reaction that has been known since 1957, i.e., one of the first photoreactions reported, to provide an interesting source of functionalized guaianolide sesquiterpene lactones. 25,26 This reaction was optimized in a previous project in which an extensive study of the reaction conditions permitted the synthesis of guaianolide 15 in 75% yield using α-santonin (11). However, when 13 was subjected to these reaction conditions, the yield decreased considerably to 30%, which is similar to that reported by Barbosa et al 27 With the aim of achieving better results, an alternative route (pathway B) was devised in which the isophotosantonin (15) (75% yield) was prepared before modifying the C-11−C-13 bond, as shown in Scheme 3.…”