楽満 憲太

Abstract Alstrostine A and isoalstrostine A are monoterpenoid indole alkaloid glycosides with unique structures found in the plant families Apocynaceae and Rubiaceae. With molecular weights exceeding 900, nine chiral centers (excluding sugar rings), and complex fused‐ring structures, the structural elucidation of these molecules using spectral analysis is highly challenging. Therefore, their structural identification through total synthesis is important in both natural product chemistry and synthetic organic chemistry. In this study, we successfully accomplished the first asymmetric total syntheses of these alkaloids in 18 or 19 steps. A key synthetic feature was a two‐ or three‐component coupling reaction between secologanin and a pyrrolidinoindoline moiety based on our proposed biosynthetic pathway. This approach enabled the synthesis of all isomers of the pyrrolidinoindoline ring, which constitutes the upper fragment of the alstrostines, and allowed us to revise the stereochemistry of alstrostine A. Additionally, a compound previously isolated as alstrostine A from Palicourea luxurians (Rubiaceae) was successfully reidentified and renamed as epialstrostine A.

Abstract This paper addresses the geometry distortion of orthoquinone-containing phenacene-type compounds by comparing the structures of phenanthrene-9,10-dione, chrysene-5,6-dione, and picene-13,14-dione. Interestingly, the calculated geometry of chrysene-5,6-dione under the isolated state was drastically different from the experimental one observed by single-crystal X-ray analysis. Theoretical calculations suggested that the molecular geometry of the o-quinone derivatives was sensitive not only to the sterically intramolecular proximity between the carbonyl oxygen and the hydrogen atoms of the benzene rings but also to intermolecular interactions. The twist distortion affects properties such as oscillator strength and 1-electron transitions, for low-lying excited states.