First Enantioselective Synthesis and Absolute Stereochemistry Assignment of New Monocyclic Sesquiterpenes from Artemisia chamaemelifolia

Abstract

We herein report the first enantioselective synthesis of two new monocyclic sesquiterpenes from Artemisia chamaemelifolia starting from an enantiopure building block. The key feature of the present approach is to allow complete control of all the stereogenic centers present in the natural products and to elucidate their absolute stereochemistry, which to date is unknown.

Determination of type B fumonisin mycotoxins in maize and maize‐based products by liquid chromatography/tandem mass spectrometry using a QqQlinear ion trap mass spectrometer

“…Originally Marco and co‐workers did not establish the C‐9 stereochemistry of the metabolite found in A. chamaemelifolia 18. Recently, however, Uttaro et al have demonstrated the 9 R stereochemistry of the natural product by means of chemical synthesis and X‐ray crystallographic analysis 20. In our epimeric mixture ( 24 ) the NMR signals corresponding to the major component matched those of the natural metabolite,18 whereas the signals of the minor one agreed closely with those of the 9 S isomer 20.…”

Titanocene‐Catalyzed Cascade Cyclization of Epoxypolyprenes: Straightforward Synthesis of Terpenoids by Free‐Radical Chemistry

“…[18] Recently, however, Uttaro et al have demonstrated the 9R stereochemistry of the natural product by means of chemical synthesis and X-ray crystallographic analysis. [20] In our epimeric mixture (24) the NMR signals corresponding to the major component matched those of the natural metabolite, [18] whereas the signals of the minor one agreed closely with those of the 9S isomer.…”

Lipases-Promoted Enantioselective Syntheses of Monocyclic Natural Products

“…In the final step, treatment of (-)- (14) with the salt-free Wittig reagent gave crystalline karahana lactone (-)-(2). Purification by recrystallization improved the optical purity of (-)-(2) (ee>99%).…”

“…This ketol was converted into the single trans-2-carbomethoxy-cyclohexanone (13) by the 1,4 addition of lithium dimethylcuprate, followed by the quenching with methylcyanoformate in HMPA [5]. Treatment of (13) with p-TsOH.H 2 O afforded the crystalline keto-lactone (-)- (14) as a single product. The pathway can be regarded as an acid-induced domino reaction [6] in which the subsequent reaction (cyclization by transesterification) is the result of three reactions (deprotection of (13), epimerization and cyclization).…”

“…Starting from karahana lactone (+)-(2) as the enantiopure building block for the introduction and determination of the absolute stereochemistry, we have carried out the first enantioselective synthesis of (+)-(4) [14] to confirm the structural assignment and to determine the absolute stereochemistry of the four chiral centers present in the natural product. Our methodology is depicted in (Scheme 4).…”