NMR investigations of forskolin. Complete assignment of proton and carbon NMR spectra and conformational analysis

Kogler, Herbert; Fehlhaber, H.‐W.

doi:10.1002/mrc.1260291004

Cited by 18 publications

(10 citation statements)

References 30 publications

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“…The H-6˛proton of 1 appeared downfield shifted (υ 6.20) with respect to that of 4 (υ 4.44). 13 The C-1-C-4 and C-8-C-20 carbon atom resonances of 1 (Table 2) were almost identical with those of 4, 13 whereas the observed differences in the chemical shifts of the C-5, C-6 and C-7 carbons [υ D υ 1 υ 4 : 0.2, C1.2 and 1.6 ppm, respectively] are compatible only with the presence in 1 of an acetoxyl substituent at the 6ˇ-position. Finally, the gHMBC spectrum of 1 showed connectivity between the carbonyl carbon of the 6-O-acetyl group (υ 170.49 s) and the H-6˛proton (υ 6.20 dd), which, in turn, was connected with the C-5, C-7, C-8 and C-10 carbons, whereas the H-7˛proton showed gHMBC cross peaks with the carbonyl carbon of the other acetate (υ 170.31 s) and the C-6, C-8, C-9 and C-17 carbons.…”

Section: Resultsmentioning

confidence: 97%

“…The IR spectrum of 3 was devoid of hydroxyl absorptions, whereas 2 596 Spectral Assignments and Reference Data showed a hydroxyl band at 3468 cm 1 . The C-9 methine carbon of 3 appeared at υ 57.32 in its 13 C NMR spectrum and it was connected (gHSQC) with one proton singlet signal resonating at υ 3.32. In the gHMBC spectrum of 3, the H-9 proton showed connectivities with the C-1, C-5, C-7, C-8, C-11, C-17 and C-20 carbons.…”

Section: Resultsmentioning

confidence: 99%

“…Compound 2 is the 1-O-acetyl derivative of 1, as was evidenced by its molecular formula (C 26 H 38 O 9 ) and the presence of three acetoxyl groups in its 1 H and 13 Table 1) and 4 (υ 4.54 ddd), 13 together with the diamagnetic shift of the C-2 carbon of 2 (υ 23.11) with respect to those of 1 (υ 27.06) and 4 (υ 26.46), 13 strongly supported that 2 is 1,6-di-O-acetylforskolin.…”

Section: Resultsmentioning

confidence: 99%

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Structural and spectral assignment of three forskolin‐like diterpenoids isolated from Plectranthus ornatus

Rijo

Simões

Rodrı́guez

2005

Magnetic Reson in Chemistry

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Three labdane diterpenoids were isolated from an acetone extract of Plectranthus ornatus. Their structures, closely related to that of forskolin, were determined by NMR studies. Unambiguous and complete assignments of the 1H and 13C NMR chemical shifts for these substances are presented. The assignments are based on 2D shift-correlated [1H, 1H-COSY, 1H, 13C-gHSQC-1J (C,H), 1H, 13C-gHMBC-(n)J (C,H) (n = 2 and 3)] and NOE experiments.

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Section: Resultsmentioning

confidence: 97%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Structural and spectral assignment of three forskolin‐like diterpenoids isolated from Plectranthus ornatus

Rijo

Simões

Rodrı́guez

2005

Magnetic Reson in Chemistry

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“…Therefore, the chemical structure of 1 was elucidated as 6b-acetoxy-7b-hydroxy-8,13-epoxy-labd-14-en-11-one-1a -O-b -D-glucopyranoside. 14,15) The aglycon of 1, 9-deoxy coleonol B, was synthesized many years ago without any reported NMR data. 5.73 (1H, br s) and 3.47 (1H, s) were assigned to be H-1, H-5, H-6, and H-9, respectively, by their HMQC and HMBC correlations and comparing with those of 1.…”

Section: Diterpenes From Coleus Forskohlii (Willd) Briq (Labiatae)mentioning

confidence: 99%

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

Shan

Liu

et al. 2008

CHEMICAL & PHARMACEUTICAL BULLETIN

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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.

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“…The orientations of 1b-H, 6a-H and 7a-H were confirmed by the coupling constants in 1 H-NMR and the NOEs of H-1/H 3 -20, H-5/H-6, H-5/H-7 and H-6/H-7. 15,16) 16,17) allowing the assignment of the ring conjunction as trans-form for both A/B and B/C. Therefore, the chemical structure of 1 was elucidated as 6b-acetoxy-7b,9a-dihydroxy-8,13-epoxylabd-14-en-11-one-1a-O-b-D-glucopyranoside.…”

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confidence: 99%

Two Minor Diterpene Glycosides and an Eudesman Sesquiterpene from Coleus forskohlii

Shan

Wang

Zhou

et al. 2007

CHEMICAL & PHARMACEUTICAL BULLETIN

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Coleus forskohlii (WILLD.) BRIQ. (Labiatae) is largely distributed over the tropical and subtropical regions of India, Pakistan, Sri Lanka, tropical East Africa and Brazil, and it has been used since ancient times for medical treatment in Hindu and Ayurvedic traditional medicine.1,2) Its characteristic constituents, 8,13-epoxy-labd-14-en-11-one diterpenes, especially the main constituent forskolin, showed positive inotropic, antihypertensive and adenylatecyclase stimulating activities.2-12) The plant was later found in Yunnan Province of China and its aqueous extract has been used as a natural medicine to cure asthma, cough, acute and chronic bronchitis. [10][11][12] Up to now, almost the whole studies have been concentrated on these lipophilic labdane diterpene aglycones, and only two previous studies reported the polar fraction of the whole plant extract, from which only caffeic acid and two monoterpene glycosides were obtained. 13,14) In order to discover more novel and active compounds, further examination of the polar fraction has yielded two new diterpene glycosides, forskoditerpenosides A, B (1, 2) and a new eudesmane sesquiterpene, 4b,7b,11-enantioeudesmantriol (3), whose structures were established on the basis of 1D, 2D NMR and HR-ESI-MS. The relative configuration of 3 was further confirmed by single-crystal X-ray diffraction. Their isolation and structural elucidation are reported below. Compounds 1 and 2 were tested for effect on isolated guinea pig tracheal spirals in vitro. Results and DiscussionThe 95% EtOH extract of the whole plant of C. forskohlii afforded compounds 1-3, which were identified as 6b-acetoxy-7b,9a-dihydroxy-8,13-epoxy-labd-14-en-11-one-1a-Ob-D-glucopyranoside (1), 6b,7b-diacetoxy-9a-hydroxy-8,13-epoxy-labd-14-en-11-one-1a-O-b-D-glucopyranoside (2), and 4b,7b,11-enantioeudesmantriol (3).Forskoditerpenoside A (1) . These spectral data were consistent with the characteristics for 8,13-epoxy-labd-14-en-11-one type diterpenes. 8-12)The 1 H-NMR signal at d 5.74 (1H, dd, Jϭ2.8, 4.8 Hz) was assigned to H-6 by its coupling constants. 15,16) The chemical shifts of H-6 and C-6 suggested that an acetyl group was attached to C-6, as confirmed by the cross-peak between d H 5.74 and d C 171.2 in the HMBC spectrum (Fig. 2). Then, the signals at d 2.39 (1H, d, Jϭ2.8 Hz) and 4.28 (1H, d, Jϭ4.8 Hz) were assigned to H-5 and H-7, respectively, interpreted from their coupling constants as well as HMQC and HMBC correlations.15) The signal at d 4.33 (1H, br s), which showed long-range correlations with C-2, C-3, C-5, C-10 and C-20 in the HMBC spectrum, was attributed to H-1, correlated to C-1 at d 86.5 in HMQC spectrum. According to the above analysis, the structure of 1 was very similar to that of coleonol B isolated from this plant earlier, in exception of a signal for an anomeric proton at d 4.21 (1H, d, Jϭ7.8 Hz), linked to the anomeric carbon at d 106.0 in its HMQC spectrum, as well as five oxygenated carbons between d 63.7 and 79.0 and six proton signals between d 3.17 and 3.81. Combining the Mo...

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NMR investigations of forskolin. Complete assignment of proton and carbon NMR spectra and conformational analysis

Cited by 18 publications

References 30 publications

Structural and spectral assignment of three forskolin‐like diterpenoids isolated from Plectranthus ornatus

Structural and spectral assignment of three forskolin‐like diterpenoids isolated from Plectranthus ornatus

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

Two Minor Diterpene Glycosides and an Eudesman Sesquiterpene from Coleus forskohlii

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