Enantioselective Syntheses and Absolute Configuration of the Ladybird Defence Alkaloids (+)-Calvine and (+)-2-Epicalvine

Abstract

Enantiomerically pure (+)-calvine (1a) and (+)-2-epicalvine (1b), two piperidine alkaloids isolated from ladybird beetles of the genus Calvia (Coccinellidae), were synthesized by two different strategies starting from (−)-2,3,6,7,8,8a-hexahydro-3-phenyl-5H-[1,3]oxazolo[3,2-a]pyridine-5-carbonitrile (2).The key steps of these syntheses are the stereocontrolled formation of an asymmetric centre α to the nitrogen atom of

Synthesis and Absolute Configuration of Hyperaspine, an Alkaloid of the Ladybird Hyperaspis campestris

“…It is interesting to mention that (+)-hyperaspine has the same absolute configuration at C-8 than the related ladybird alkaloids (+)-calvine and (+)-2-epicalvine [11] suggesting a possible biogenetic relationship between these alkaloids.…”

Anodic Oxidation as an Enabling Tool for the Synthesis of Natural Products

“…71 Similarly, anodic oxidation of chilenamine (10) to the hydroxyisoindolo-benzazepine 11 and further Ley-Griffith oxidation 73 delivered lennoxamine (12) in 63% yield over two steps (Scheme 2). 70 The Shono oxidation, especially the -functionalization of amines, has been applied in a variety of natural product syntheses, including for instance nazlinine (13), 74 (+)myrtine 14, 75 (+)-calvine (15), 76 (+)-crispine A (16), 77…”

Synthesis of 2,6-disubstituted piperidine alkaloids from ladybird beetles Calvia 10-guttata and Calvia 14-guttata

“…5 The absolute configuration was determined by enantioselective total synthesis. 6 Since then, only one other preparation of 1 has appeared 7 along with two formal syntheses. 8 All but one approach known so far used alkaloids 3 and/or 4 as key intermediates for the (formal) syntheses of 1 and/or 2.…”

“…8 All but one approach known so far used alkaloids 3 and/or 4 as key intermediates for the (formal) syntheses of 1 and/or 2. 5,6,8 Recently, we have communicated racemic syntheses of calvine and epicalvine. 9 In this full account, we wish to report short and efficient stereoselective total syntheses of all four naturally occurring piperidine alkaloids 1-4.…”