Diterpenes from Coleus forskohlii (WILLD.) BRIQ. (Labiatae)

Abstract

Coleus forskohlii (WILLD.) BRIQ. (Labiatae) has been used for medical treatment in Hindu and Ayurvedic traditional medicine from ancient times. 1) Since its major constituent forskolin was discovered to have positive inotropic, antihypertensive, and adenylatecyclase-stimulating activities, it has ever aroused a great deal of scientific interest, and many 8,13-epoxy-labd-14-en-11-one diterpenes have been obtained.1-11) The plant was subsequently found in Yunnan Province of China, while the major diterpene was determined to be coleonol B.10,11) So as to discover more novel and active compounds, further examination of the polar fraction of the whole plant extract has been carried out and yielded two new diterpene glycosides and a sesquiterpene in our earlier research.12) Continuing work yielded three other new diterpene glycosides forskoditerpenosides C, D, and E (1-3) and a diterpene forskoditerpene A (4). Complete NMR data studies on each compound were performed unambiguously to determine the structures of the compounds and to assign all the proton and carbon resonances. The isolation and structural elucidation of them are reported below. Forskoditerpenosides C, D, and E (1-3) were tested for their effects on isolated guinea pig tracheal spirals in vitro. Results and DiscussionAir-dried whole plants of C. forskohlii were extracted with EtOH three times. The concentrated extract was dissolved in water and successively extracted with petroleum ether (60-90°C) and n-BuOH. The n-BuOH soluble fraction was extracted with H 2 O in reflux and the combined solution was separated by means of various chromatographic procedures to afford four labdane diterpenes (1-4). . According to these spectral data, 1 was considered to be a 8,13-epoxy-labd-14-en-11-one diterpene. [1][2][3][4][5][8][9][10][11] The 1 H-NMR signal at d 5.71 (1H, dd, Jϭ4.0, 2.4 Hz) was assigned to H-6 by its coupling constants. 13,14) The chemical shifts of H-6 and C-6 suggested that Pharmacy, Meijo University; Tempaku, Nagoya 468-8503, Japan. Received August 6, 2007; accepted September 25, 2007 Three new minor labdane diterpene glycosides, forskoditerpenoside C, D, and E (1-3), and a novel labdane diterpene forskoditerpene A (4) were isolated from the ethanol extract of the whole plant of Coleus forskohlii. Their structures and relative stereochemistry were elucidated on the basis of extensive spectroscopic analyses including 1D-, 2D-NMR, and HR-ESI-MS experiments. Compounds 1-3 showed an unusual 8,13-epoxy-labd-14-en-11-one glycoside pattern. They showed relaxative effects on isolated guinea pig tracheal spirals in vitro. Compound 4 with a cyclopropyl, confirmed by a single-crystal X-ray diffraction determination, is the first known labdane derivative with a spiro element.

Plectranthus barbatus: A Review of Phytochemistry, Ethnobotanical Uses and Pharmacology – Part 1

“…2 8,13-Epoxylabd-14-en-11-one diterpenoids. (67), and E (68) were isolated from the whole plant of P. barbatus grown in China [61,63] (l " Table 1, Fig. 5).…”

Myrothecoside, a Novel Glycosylated Polyketide from the Terrestrial FungusMyrotheciumsp. GS-17

“…The 1 H‐NMR (600 MHz, (D 5 )pyridine) spectrum of myrothecoside (Table) indicated the presence of a methoxy group at δ 3.77 (3 H, s ), two oxymethines at δ 4.95 (1 H, m ), 4.79 (1 H, m ), two cis ‐olefinic H‐atom at δ 5.59 (1 H, dt , J = 9.7 Hz, 3.4 Hz), 5.43 (1 H, d , J = 9.7 Hz), two trans ‐olefinic H‐atom at δ 5.94 (1 H, dd , J = 15.2 Hz, 10.3 Hz), 5.39 (1 H, dd , J = 15.2 Hz, 8.0 Hz), and two amino H‐atom δ 8.25 (1 H, s ) and 7.86 (1 H, s ). Twenty‐seven C‐atom signals were evident in the 13 C‐NMR spectrum (150 MHz, (D 5 )pyridine) of myrothecoside (Table) and deduced to be four olefinic CH carbons at δ (C) 128.5, 132.9, 133.0, 140.8, one C=O carbon at δ (C) 175.6, and six oxygenated carbons at δ (C) 98.5(C(1′′)), 73.1(C(2′′)), 76.1(C(3′′)), 79.1(C(4′′)), 78.3(C(5′′)), and 62.6(C(6′′)) accounted for by a mannose residue .…”

A New Configurational Analysis of 1,6,7-triacetoxy-8,13-epoxy-14-labden-11-one Isolated from Plectranthus ornatus Based on NMR and Theoretical Calculations

“…Although the 1D ( 1 H and 13 C) and 2D ( 1 H-1 H COSY, 1 H-13 C HSQC, and 1 H- 13 C HMBC) NMR analyses of the labdane diterpenoid isolated from P. ornatus are in agreement for 1, the configurations of C-8 and C-13 have not been confirmed. The stereochemistry of the forskolin derivatives is normally deduced by NOESY experiment [6][7][8][9] and the exciton chirality circular dichroism method [6]. The R configuration of C-13 in these forskolin-type skeletons was confirmed Fig.…”