Two Novel ent‐Kaurene Diterpenoids from Isodon rubescens

Abstract

A novel 20‐nor‐ent‐kaurene diterpenoid, rubescensin N (1), and a new 7,20‐epoxy‐ent‐kaurene diterpenoid, rubescensin O (2), along with the seven known diterpenoids rabdoternins A–F and xerophilusin N, were isolated from Isodon rubescens collected in Jiyuan prefecture, Henan Province, China. Their structures were established by extensive spectroscopic analysis. Compound 1 is the first example of a naturally occurring 20‐nor‐ent‐kaurene diterpenoid from the Isodon genus plants.

Cytotoxic ent-kauranoid derivatives from Isodon rubescens

“…Careful analysis of the NMR data of the diterpene part indicated that it was a 7,20-epoxy-kauranoid due to the characteristic signal of a hemiketal carbon (C-7 at d C 100.5). Comparison of the 1 H and 13 C NMR data of the diterpene part with those of rabdoternins E (14) and F (13), two known 7,20-epoxykauranoids that had been isolated as well, suggested that the diterpene part in 1 was strongly resembling to that of rabdoternin F (13). 10 Further analysis of 2D NMR data allowed us to determine the gross structure of the diterpene part as shown in Figure 1.…”

“…The NMR spectroscopic data of 4 were closely identical to those of 2 (Table 2), except for the substitution group at C-20. Besides the signals for diterpene moiety, the 13 C NMR and DEPT spectra of 4 ( Table 2) …”

A new rearranged and a new seco-ent-kaurane diterpenoids from Isodon parvifolius

“…Thus far, more than 500 new ent-kaurane diterpenoids have been isolated from the genus Isodon by our group, 1 including many interesting novel ent-kaurane diterpenoids such as 1:1 complexes of natural ent-kauranoids, 2 a natural equimolecular mixture of two epimeric ent-kauranoids, 3 6,7:8,15-seco-ent-kauranoids, 4 8,15-seco-ent-kauranoids, 5 15,16-seco-ent-kauranoid, 5 20-nor-ent-kauranoid, 6 symmetric and asymmetric dimeric ent-kauranoids, 7 and novel C 19 skeleton ent-kauranoid. 8 Many of these diterpenoids display various biological activities, such as antibacterial, 9 anti-inflammatory, 10 and especially antitumor actions.…”

Ent-Kaurane Diterpenoids from Isodon rubescens var. rubescens

“…To further examine the chemistry of this species in the Dabie Mountains, we collected some plant materials in the southeastern mountains. Besides xindongnins A and B (6, 7), five new 20-non-oxygenated ent-kauranoids (1)(2)(3)(4)(5) and three known analogues melissoidesin G (8), 8) dawoensin A (9), 9) and glabcensin V (10), 10) were isolated from this plant. The structures of the five new compounds were determined by analysis of their spectral data, especially two dimensional (2D) NMR spectra.…”

“…[1][2][3][4][5][6] Xindongnins A and B, two 20-nonoxygenated ent-kaurane diterpenoids, were regarded as the major constituents of I. rubescens var. rubescens, 7) which was collected in Xin Prefecture, the northwestern part of the Dabie Mountains.…”