Enantioselective Total Syntheses of (R)‐ and (S)‐Naphthotectone, and Stereochemical Assignment of the Natural Product

Abstract

Both isomers of naphthotectone, an isoprenoid quinone from Verbenaceae Tectona grandis possessing interesting biological activities, were enantioselectively obtained by two different synthetic routes in which the carbon side-chain of the naphthoquinone core was introduced using either a Sonogashira or a Heck coupling reaction. In both cases, the naphthoquinone core of the final products was obtained by a late-stage

Bioactive Constituents from the Aerial Parts of Pluchea indica Less

“…The ESI-Q-Orbitrap MS { m / z 301.08969 [M + H] + (calcd for C 17 H 17 O 3 S, 301.08929)} and 1 H-, 13 C- ( Table 4 , CD 3 OD), 2D- ( 1 H- 1 H COSY, HSQC, HMBC) NMR experiments suggested that there was one more acetyl group [δ H 2.07 (3H, s, H 3 -2′′′), δ C 172.3 (C-1′′′)] at C-4′′ of aglycone than 3 . Finally, comparing the optical rotation { − 8.9° (MeOH)} with reference [ 36 ], the absolute configuration of 4 was revealed to be 3′′ S . Thus, its structure was determined as 3′′-ethoxy-(3′′ S )-pluthiophenol-4′′-acetate.…”

“…Consequently, the planar structure of 1 was determined. Finally, through the comparison of the optical rotation { + 11.4° (MeOH)} of 1 with those of ( R )- and ( S )-(3 E )-2-hydroxy-2-methyl-4-[1,8:4,5-bis(methylenedioxy)-2-naphthyl]but-3-enyl acetate, { R : + 22.6° (MeOH); S : − 20.0° (MeOH)], respectively} [ 36 ], its absolute configuration was elucidated to be 3′′ R .…”

“…The acetyl group was elucidated to substitute in C-4′′ by the long-range correlations observed from H-4′′ to C-1′′′ in the HMBC experiment. Similarly, according to the optical rotation, the absolute configuration of 2 was determined to be 3′′ R [ 36 ], and its structure was determined to be (3′′ R )-pluthiophenol-4′′-acetate.…”

“…The planar structures of 1 and 2 had been reported by Bitew et al [ 37 ], while their absolute configurations were not being determined. Here, they were clarified by the comparison of optical rotation with those of known compounds [ 36 ] for the first time.…”

“…The ethoxy was clarified to link to C-3′′ position by the long-range correlation observed from δ H 3.55, 3.83 (H 2 -5′′) to δ C 15.5 (C-6′′), 72.7 (C-3′′). At last, its absolute configuration was elucidated to be 3′′ S by the optical rotation { − 16.7° (MeOH)} determination [ 36 ].…”