Reactions of forskolin, a biologically active diterpenoid from Coleus forskohlii

Bhat, Sujata V.; Bajwa, Balbir S.; Dornauer, Horst; Souza, N. J. De

doi:10.1039/p19820000767

Cited by 53 publications

(24 citation statements)

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“…In the most recent and arguably most impressive example, a series of polyglycosides were oxidized by Waymouth’s catalyst in 30–60% yields at the terminal sugar 23 . Prior to this study, the polyketide antibiotic mupirocin methyl ester was oxidized by the combination of TEMPO ((2,2,6,6-tetramethylpiperidin-1-yl)oxyl), NaOCl and KBr to give only a 31% yield of a monooxidation product 24 , and the labdane diterpene forskolin was oxidized by stoichiometric CrO 3 /pyridine in an 80% yield 25 , whereas another labdane diterpene, andrographolide, was oxidized to the 3-ketone in only a 5% yield under the optimized conditions 26 . These studies illustrate that the conditions developed for the reaction of one structure do not translate into the oxidation of another structure of the same or different class, and some molecules have resisted selective oxidation under all known conditions 27–29 .…”

Section: Resultsmentioning

confidence: 99%

Site-selective oxidation, amination and epimerization reactions of complex polyols enabled by transfer hydrogenation

Hill

Hartwig

2017

Nature Chem

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Polyoxygenated hydrocarbons that bear one or more hydroxyl groups comprise a large set of natural and synthetic compounds, often with potent biological activity. In synthetic chemistry, alcohols are important precursors to carbonyl groups, which then can be converted into a wide range of oxygen- or nitrogen-based functionality. Therefore, the selective conversion of a single hydroxyl group in natural products into a ketone would enable the selective introduction of unnatural functionality. However, the methods known to convert a simple alcohol, or even an alcohol in a molecule that contains multiple protected functional groups, are not suitable for selective reactions of complex polyol structures. We present a new ruthenium catalyst with a unique efficacy for the selective oxidation of a single hydroxyl group among many in unprotected polyol natural products. This oxidation enables the introduction of nitrogen-based functional groups into such structures that lack nitrogen atoms and enables a selective alcohol epimerization by stepwise or reversible oxidation and reduction.

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Section: Resultsmentioning

confidence: 99%

Site-selective oxidation, amination and epimerization reactions of complex polyols enabled by transfer hydrogenation

Hill

Hartwig

2017

Nature Chem

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“…6 This is the first report on 1-3 as naturally occurring substances, although they are already known as semisynthetic derivatives. 6-O-Acetylforskolin (1) and 1,6-di-Oacetylforskolin (2) have previously been obtained by acetylation of forskolin (4), 7 whereas 3 (1,6-di-O-acetyl-9-deoxyforskolin) has been reported as an intermediate in a semisynthesis of 4 starting from 9-deoxyforskolin (5). 8,9 Structures 1-3 were established by NMR spectroscopic studies and, since only partial 1 H NMR data for 1 and 2 had been reported, 7 we decided to perform the complete assignment of the 1 H and 13 C NMR spectra of these substances in order to provide several sets of data that might serve as models for future assignments of other structurally related compounds.…”

Section: Introductionmentioning

confidence: 99%

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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“…(1H, br s, 1b-H), 1.99 (1H, m, 2a-H), 2.03 (1H, m, 2b-H), 1.00 (1H, m, 3a-H), 1.06 (1H, m, 3b-H Oxidation of 4 and 5 The oxidation of 4 and 5 was performed following the procedure described by Bhat et al 19) To a stirred suspension of Collins reagents (8.0 mg) in methylene chloride (3 ml) was added a solution of 4 (4.0 mg) and 5 (2.7 mg) in methylene chloride (2 ml), respectively. The mixture was stirred at room temperature for 2.5 h and filtered.…”

Section: Methodsmentioning

confidence: 99%

“…Forskoditerpenoside B (2) 19,20) The sugar moiety was identified as b-Dglucopyranoside by acid hydrolysis and the coupling constant (Jϭ7.7 Hz) of H-1Ј. As listed in Table 2, the downfield shift of ϩ10.9 (d 85.5) observed for C-1, compared with that in 6-acetylforskolin, and correlation in the HMBC spectrum between C-1 and H-1Ј, indicated that the glucose was attached to C-1.…”

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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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Reactions of forskolin, a biologically active diterpenoid from Coleus forskohlii

Cited by 53 publications

References 0 publications

Site-selective oxidation, amination and epimerization reactions of complex polyols enabled by transfer hydrogenation

Site-selective oxidation, amination and epimerization reactions of complex polyols enabled by transfer hydrogenation

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

Two Minor Diterpene Glycosides and an Eudesman Sesquiterpene from Coleus forskohlii

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