New <i>ent</i>-Abietane and <i>ent</i>-Kaurane Diterpenoids from <i>Isodon rubescens</i>

Abstract

Five new ent-abietane diterpenoids, ent-abierubesins A-E (1-5), and two new ent-kauranoids, hubeirubesins A and B (6, 7), together with three known diterpenoids (8-10), were isolated from the aerial parts of Isodon rubescens. Their structures were identified by means of extensive spectroscopic analysis, and the absolute stereochemistry of 1 was determined by single-crystal X-ray diffraction experiment. Isodon rubescens; ent-abietane; ent-abierubesin; ent-kaurane; hubeirubesin As an important class of diterpenoids, ent-abietanoids are not so widely spread and structurally diverse as their enantiomers, abietanoids. Among ent-abietanes, 12,17-olide-type ones are in a majority and isolated from plants of Euphorbiaceae and Acanthaceae families. Key words1) However, another type of ent-abietanes without 12,17-olide moieties have been obtained from the genus Isodon of Lamiaceae family.2,3) Our previous investigations on chemical constituents of Isodon rubescens (Hemsl.) Hara yielded mainly ent-kauranoids. [4][5][6] However, five new ent-abietanoids, ent-abierubesins A-E (1-5), and two new ent-kauranoids, hubeirubesins A and B (6, 7), together with another three known diterpenoids (8-10), were isolated from this species in our present research. Although belonging to ent-abietanes, compound 5 was quite different from other ent-abietanes (1-4, 8, 9) in functional groups of A-and B-rings. In contrast, 5 exhibited the same structural characteristics (even including the configuration of C-16) as the known ent-kauranoid (10) so that 5 might be assumed as an 8,15-seco product of 10. Current paper describes the isolation, structure elucidation, and cytotoxic evaluation of selected compounds. Results and DiscussionThe aerial parts of I. rubescens (10 kg) were extracted with 90% aqueous EtOH at room temperature and then the extract was partitioned between EtOAc and H 2 O. Repeated chromatography of the EtOAc soluble portion (550 g) yielded five new (1-5) and two known (8, 9) ent-abietane diterpenoids, together with two new (6, 7) and one known (10) ent-kaurane diterpenoids (Fig. 1). By comparing the spectroscopic data with literature values, three known compounds (8-10) were identified as hebeiabinin B (8), 7) ent-abienervonin C (9), 8) and rubescensin G (10), 9) respectively. ent-Abierubesin A (1) was obtained as colorless pieces in MeOH. The molecular formula was determined by positive high resolution-electrospray ionization mass spectrometry C-NMR and distortionless enhancement by polarization transfer (DEPT) spectra of 1, signals of a ketone carbonyl, a trisubstituted olefine, nine methylenes (including three oxygenated ones), three methines, one oxygenated and two nonoxygenated quaternary carbons, and two methyl groups were present (Tables 1, 3). Compound 1 retained three degrees of unsaturation except above-mentioned olefinic and carbonyl groups, and lacked one nonoxygenated quaternary carbon relative to the classical entkaurane skeleton, suggesting 1 to be a tricyclic diterpenoid.Comparison of NMR spectra of 1 and the ...

Lasiokaurin Regulates PLK1 to Induce Breast Cancer Cell G2/M Phase Block and Apoptosis

“…Isodon rubescens is a traditional Chinese herbal medicine containing a wide range of bioactive components, including terpenoids, flavonoids, alkaloids, polysaccharides, amino acids, and some others [9][10][11][12]. It has been proven that possesses antitumour [13][14][15], anti-bacterial [16][17][18], anti-oxidization [19] and immune-enhancing properties through modern pharmacological research and clinical trials.…”

Diterpenoids from Isodon rubescens and their nitric oxide production inhibitory activity

“…11,12 Furthermore, the chemical constituents of I. rubescens collected from Hubei Province have not been extensively investigated, only 16 new diterpenoids have been reported, including diterpene alkaloids with an azaent-kaurane skeleton. [13][14][15][16][17] Therefore, in order to fully understand the active constituents of I. rubescens from different regions, a reinvestigation of I. rubescens collected from Badong county, Hubei Province was undertaken in the hope of discovering diterpenoids with interesting structures and biological activities. As a result, six new diterpenoids (1-6), together with twenty-ve known ent-kaurane diterpenoids (7-31), a known ent-atisane diterpenoid (32) and two known ent-abietane diterpenoids (33)(34) were isolated from this plant, and it should be noted that compounds 10, and 13-17 have been reported in our previous work.…”

Antitumor and Antibacterial Derivatives of Oridonin: A Main Composition of Dong-Ling-Cao

“…It is also a kind of antibiotic and antiphlogistic folk medicine and was first listed in Pharmacopoeia of the People’s Republic of China in the year 1977. The major chemical composition of I. rubescens is diterpenoids, such as oridonin, ponicidin, pedalitin, taibairubescensins A and B, xindongnins A and B, and so on [1,2,3,4,5,6,7,8]. Of these, oridonin is the major and most important ingredient of this medicinal tea.…”