Synthesis of (+)-Strigol and (+)-Orobanchol, the Germination Stimulants, and Their Stereoisomers by Employing Lipase-Catalyzed Asymmetric Acetylationas the Key Step

Abstract

The potent seed germination stimulants (+)‐strigol (1), (+)‐orobanchol (2) and their stereoisomers [2′‐epistrigol (1′), ent‐1, ent‐1′, 2′‐epiorobanchol (2′), 4‐epiorobanchol (2′′) and 4, 2′‐bisepiorobanchol (2′′′)] were prepared from the enantiomers of 3, which were obtainable by lipase‐catalyzed enantiomer separation of (±)‐3.

Ent-2′-epi-Orobanchol and Its Acetate, As Germination Stimulants for Striga gesnerioides Seeds Isolated from Cowpea and Red Clover

“…The [α] D value of acetylated (+)-orobanchol was +148° ( c 0.054, CHCl 3 ) . The optical rotation of compound 13 showed an [α] D value of −58° ( c 0.023, CHCl 3 ), whereas the [α] D value of (+)-2′- epi -orobanchol reported previously was +71° ( c 0.30, CHCl 3 ) . Therefore, we concluded that compounds 12 and 13 are (+)-(3a R ,4 R ,8b R ,2′ R )- ent -2′- epi -orobanchyl acetate and (−)-(3a R ,4 R ,8b R ,2′ R )- ent -2′- epi -orobanchol, respectively (Figure ).…”

“…Journal of Agricultural and Food Chemistry ARTICLE reported previously was +71°(c 0.30, CHCl 3 ). 27 Therefore, we concluded that compounds 12 and 13 are (+)-(3aR,4R,8bR,2 0 R)ent-2 0 -epi-orobanchyl acetate and (À)-(3aR,4R,8bR,2 0 R)-ent-2 0 -epiorobanchol, respectively (Figure 5).…”

Total Synthesis of Strigolactones via Palladium-Catalyzed Cascade Carbonylative Carbocyclization of Enallenes

“…Subsequently, the C-ring moiety was obtained through a one-pot procedure encompassing ester hydrolysis, NaBH 4 reduction, and lactone formation, giving 2d in 73% yield. Armed with these findings, we successfully synthesized both rac -GR-24 ( rac - 1d ) and rac - epi -GR-24 ( rac - 1e ), adhering to a previously reported procedure but with minor modifications …”

Germination stimulant from root exudates of Vigna unguiculata

“…Since there were remarkable differences in the resonances of H-9 between 5 (d 7.46) and (+)-2-epiorobanchol (6, Fig. 1) (d 7.50-7.52), which was synthesized (Hirayama and Mori 1999), but not between 5 and 3, the structure of 5 was determined to be (+)-4-Oacetylorobanchol (Fig. 2).…”

“…The absolute configuration of (+)-orobanchol (3) was revealed as shown in Fig. 1, and its [a] D was reported to be +158°(c 0.38, CHCl 3 ) (Hirayama and Mori 1999). Although the optical rotation of 5 showed [a] D +20°(c 0.30, CHCl 3 ), the absolute configuration of 5 could not be determined due to the structural difference between 3 and 5.…”