Correlation of configuration and fluorine-19 chemical shifts of .alpha.-methoxy-.alpha.-trifluoromethylphenyl acetate derivatives

Sullivan, G.; Dale, James A.; Mosher, Harry S.

doi:10.1021/jo00952a006

Cited by 521 publications

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“…The absolute configuration at C-12 of 1a (the 16-O-acetyl derivative of 1) was determined using the method first described by Mosher and colleagues 30,31 1 H NMR signals associated with the decalin ring system in the R-MTPA ester were shifted downfield relative to those of the S-MTPA ester, and the opposite was true for the resonances of the lactone ring moiety (with the exception that essentially no difference in relative shift was observed for the protons of the acetyl group). This allowed 1 to be assigned structurally as 12(S),16ξ-dihydroxycleroda-3,13-dien-15,16-olide.…”

Section: Resultsmentioning

confidence: 99%

Cytotoxic Constituents from the Fruiting Branches of Callicarpa americana Collected in Southern Florida^,1

Jones

Lobo-Echeverri

et al. 2007

J. Nat. Prod.

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Bioassay-guided fractionation of the combined fruits, leaves, and twigs (fruiting branches) of Callicarpa americana, collected from a plot in a forested area in southern Florida, led to the isolation of six new clerodane diterpenes (1-6) and eight known compounds. The structures of 1-6 [12(S), 16ξ-dihydroxycleroda-3,13-dien-15,16-olide (1), 12(S)-hydroxy-16ξ-methoxycleroda-3,13-dien-15,16-olide (2), 12(S)-hydroxycleroda-3,13-dien-15,16-olide (3), 16 ξ-hydroxycleroda-3,11 (E),13-trien-15,16-olide (4), 3β,12(S)-dihydroxycleroda-4(18),13-dien-15,16-olide (5), and 12(S)-hydroxycleroda-3,13-dien-16,15-olide (6)] were elucidated by interpretation of spectroscopic data and chemical methods. The absolute configuration at C-12 in 1 and 3 was ascertained using the Mosher ester technique. The cytotoxicity of all isolates was tested against a panel of human cancer cell lines, and compounds 1, 4, and 6, and the known compounds genkwanin, 16ξ-hydroxycleroda-3,13-dien-15,16-olide, and2-formyl-16ξ-hydroxy-3-A-norcleroda-2,13-dien-15,16-olide were active (ED 50 <5 μg/mL). However, 1 was found to be inactive against human cancer cells implanted in mice using a hollow-fiber tumor model. Callicarpa americana L. is a shrub native to the southeastern United States. 2 Although the genus has been considered traditionally as a member of the plant family Verbenaceae, molecular and micro-morphological observations have prompted contemporary taxonomic authorities to reclassify Callicarpa as a member of the family Lamiaceae. 3-5 Preparations of the bark of C. americana have been used to treat fever, 6 the leaves to treat dropsy, 7 and the roots to alleviate colic, 8 dysentery, 9 and skin cancer. 10 The roots and branches have been used in preparations intended to relieve malaria, rheumatism, and fever. 8 The leaf essential oils of C. americana have antialgal and mosquito-deterrent properties, and numerous essential oil components have been identified from the leaves of C. americana. [11][12] As part of an ongoing effort to discover novel anticancer agents from plants, 13 a chloroformsoluble extract of the combined fruits, leaves, and twigs of C. americana was investigated, using cytotoxicity against hormone-dependent prostate cancer cells (LNCaP) to guide the isolation of active constituents. This plant material was obtained from a forest plot in southern Florida using a plot-based collection method (briefly reviewed in ref. 13 ).⊥ Dedicated to the late Dr. Kenneth L. Rinehart of the University of Illinois at Urbana-Champaign for his pioneering work on bioactive natural products.*Author to whom correspondence should be addressed. Tel: (614) Results and DiscussionThe dried fruits, leaves, and twigs of Callicarpa americana L. were extracted with methanol and partitioned following a previously described protocol. 14 Based on the cytotoxic activity of the chloroform-soluble portion, bioassay-guided fractionation using a number of chromatographic techniques was carried out, guided by activity against LNCaP cells. This investigation re...

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Section: Resultsmentioning

confidence: 99%

Cytotoxic Constituents from the Fruiting Branches of Callicarpa americana Collected in Southern Florida^,1

Jones

Lobo-Echeverri

et al. 2007

J. Nat. Prod.

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“…The only substrate for BFD-H281A in the ligation with acetaldehyde was hexenal (1g) with moderate conversion to give 3g with poor enantioselectivity (entry 17). The enantioselectivity of the products obtained was determined by chiral phase HPLC and preparation of the Mosher ester derivative by reaction of (R)-3b [or (S)-3e, respectively] with Moshers acid chloride.The absolute configuration was assigned according to Moshers method, [24] showing that R-configured products arise from BAL catalysis (see entries 1, 4, 10 and 11) while the S enantiomer is gained in one case with BFDwt as a catalyst (entry 12). Surprisingly, using hexenal (1g, entry 16) and octenal (1h, entry 19), both BAL and BFDwt yielded products with the same absolute configuration as was determined by chiral phase HPLC.…”

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confidence: 99%

α,β‐Unsaturated Aldehydes as Substrates for Asymmetric CC Bond Forming Reactions with Thiamin Diphosphate (ThDP)‐Dependent Enzymes

et al. 2008

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The enzymes benzaldehyde lyase (BAL) from Pseudomonas fluorescens, benzoylformate decarboxylase (BFD) from Pseudomonas putida and pyruvate decarboxylase (PDC) from Saccharomyces cerevisiae provide different C À C bond forming possibilities of a,b-unsaturated aldehydes with aliphatic and aromatic aldehydes. Structure elucidation and determination of the absolute configuration of the products, which were obtained with high regio-and stereoselectivity were carried out. Selective 1,2-reactivity with yields of 75% and > 98% ee, for one single isomer (A) were obtained, by choosing the suitable enzyme in combination with the appropriate substrates. By varying enzymes or substrates the regioisomeric hydroxy ketones C, with up to > 99% ee, can be obtained. The application of these new chiral building blocks in the synthesis of natural products or biological active substances is considerably facilitated by applying the different ThDP-dependent enzymes as catalysts.Abbreviations: BAL, benzaldehyde lyase; BFD, benzoylformate decarboxylase; PDC, pyruvate decarboxylase; His, hexahistidine; 2-HPP, 2-hydroxy-1-phenylpropan-1-one; PAC, phenylacetylcarbinol; NTA, nitrilotriacetic acid; ThDP, thiamin diphosphate; wt, wild-type.Keywords: benzaldehyde lyase; benzoylformate decarboxylase; biocatalysts; pyruvate decarboxylase; stereochemistry IntroductionThiamin diphosphate (ThDP)-dependent enzymes are well-known to catalyse a broad range of asymmetric reactions.[1] Enzymes of this class like benzaldehyde lyase (BAL) from Pseudomonas fluorescens, [2] benzoylformate decarboxylase (BFD) from Pseudomonas putida [3] and pyruvate decarboxylase (PDC) from Saccharomyces cerevisiae [4] enable various modes of C À C bond forming reactions. Besides the physiological reactivity, several of these enzymes can catalyse, for example, the C À C bond formation between two aldehydes, giving chiral 2-hydroxy ketones with high enantioselectivity. The reactions of aromatic aldehydes as donor and aliphatic aldehydes as acceptor give rise to 2-hydroxy-1-phenyl-1-propanone derivatives with S absolute configuration in the case of BFD catalysis [5] and R for BAL.[6] If aromatic aldehydes are employed as donor and acceptor, (R)-benzoins are optained with both enzymes. [7,8] (R)-Phenylacetylcarbinol is formed in the PDC-catalysed reaction of decarboxylated pyruvate with benzaldehyde as acceptor aldehyde. [4,9] Here we describe the use of a,b-unsaturated aldehydes as substrates for C À C bond ligation in BAL-, BFD-and PDC-catalysed reactions. These substrates might act as donor and as acceptor for the 1,2-(A, C) and the 1,4-addition (B, D) (Scheme 1). Adv. Synth. Catal. 2008, 350, 759 -771 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 759 FULL PAPERSIn reactions according to Equation (1) the a,b-unsaturated aldehyde is bound to ThDP and reacts as donor resulting in the formation of hydroxy ketone A or hydroxy enone B. In reactions according to Equation (2) the a,b-unsaturated aldehyde is attacked by an "active aldehyde" and reacts as acceptor resulti...

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“…Since the original Mosher's method [46,47], NMR procedures for the assignment of absolute configuration of chiral compounds have been improved and a large number of CDAs is available for the study of different substrates. The most common one is ␣-methoxy-␣-trifluoromethyl-␣-phenylacetic acid (MTPA) known as Mosher's reagent, ␣-methoxy-␣-phenylacetic acid (MPA), ␣-methoxy-␣-(2-naphthyl)acetic acid (2-NMA), ␣-(9-anthryl)-␣-methoxyacetic acid (9-AMA), Boc-phenylglycine (BPG), among others.…”

Section: Stereochemistrymentioning

confidence: 99%

Nuclear Magnetic Resonance Spectroscopy for Structural Characterization of Bioactive Compounds

Santos

Silva

2014

Comprehensive Analytical Chemistry

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Correlation of configuration and fluorine-19 chemical shifts of .alpha.-methoxy-.alpha.-trifluoromethylphenyl acetate derivatives

Cited by 521 publications

References 0 publications

Cytotoxic Constituents from the Fruiting Branches of Callicarpa americana Collected in Southern Florida^,1

Cytotoxic Constituents from the Fruiting Branches of Callicarpa americana Collected in Southern Florida^,1

α,β‐Unsaturated Aldehydes as Substrates for Asymmetric CC Bond Forming Reactions with Thiamin Diphosphate (ThDP)‐Dependent Enzymes

Nuclear Magnetic Resonance Spectroscopy for Structural Characterization of Bioactive Compounds

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Correlation of configuration and fluorine-19 chemical shifts of .alpha.-methoxy-.alpha.-trifluoromethylphenyl acetate derivatives

Cited by 521 publications

References 0 publications

Cytotoxic Constituents from the Fruiting Branches of Callicarpa americana Collected in Southern Florida,1

Cytotoxic Constituents from the Fruiting Branches of Callicarpa americana Collected in Southern Florida,1

α,β‐Unsaturated Aldehydes as Substrates for Asymmetric CC Bond Forming Reactions with Thiamin Diphosphate (ThDP)‐Dependent Enzymes

Nuclear Magnetic Resonance Spectroscopy for Structural Characterization of Bioactive Compounds

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Cytotoxic Constituents from the Fruiting Branches of Callicarpa americana Collected in Southern Florida^,1

Cytotoxic Constituents from the Fruiting Branches of Callicarpa americana Collected in Southern Florida^,1