Studies towards the total synthesis of contignasterol

Occurrence of 2-Acetyl-1-pyrroline and Its Nonvolatile Precursors in Celtuce (Lactuca sativa L. var. augustana)

Lactuca sativa L. var. augustana has a basmati rice-like odor with a green note in the background. This typical odor is due to the release of 2-acetyl-1-pyrroline (2-AP) after heating, which is confirmed by volatile analysis. Recent metabolomic and genomic studies of different rice varieties highlighted that the presence of 2-AP was linked to the accumulation of γ-aminobutyraldehyde; genome-wide association studies also indicated that acyltransferases were involved. These results prompted us to analyze nonvolatile compound precursors in L. sativa L. var. augustana (celtuce) to search for compound derivatives with a 4,5-dioxohexan alkyl amine-like structure. Hypothetical synthetic compounds were prepared from a reductive amination between 4,5-dioxohexanal and glycine, alanine, aspartic acid, and glutamic acid to give 2-(2-acetylpyrrolidin-1-yl) alkanoic acid. We proved that 2-(2-acetylpyrrolidin-1-yl) propionic acid is present in L. sativa, which, when thermally treated, released 2-AP. Other 2-AP precursors occurring in this plant are discussed.

Two approaches to 14,15-secoergostane intermediates for the synthesis of strophasterols

Two protected 14,15-secoergostane derivatives suitable as pivotal intermediates for the synthesis of strophasterols A and B, anti-MRSA and neuronal cell-protecting natural products bearing a recently discovered strophastane skeleton, have been synthesized by two different routes. The first approach employed an oxidative cleavage of an α-hydroxy ketone intermediate with the Jones reagent as the key step to reach the targeted secoergostane from ergosterol in ten steps. In the second approach, an unprecedented reaction cascade composed of four reactions enabled us to obtain the secoergostane more efficiently in six steps.