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1.
《Tetrahedron: Asymmetry》2007,18(14):1676-1681
The achiral sesquiterpene zerumbone 1, which is readily available from wild ginger, has a unique functionality and reactivity making it a convenient starting material for its conversion into useful compounds, such as paclitaxel. Optically active triepoxyzerumbol (−)-3 and its acetate (+)-4 were synthesized by lipase-catalyzed enantioselective transesterification of racemic 3. Under optimized conditions, a lipase from Alcaligenes sp. (Meito QL) catalyzed the reaction of racemic 3 with isopropenyl acetate in THF at 35 °C to afford (1S)-3 and (1R)-4 with an E-value of 79. The absolute configuration of (1R)-4 was determined by single crystal X-ray diffraction of its ester with a chlorine atom using the anomalous dispersion effect. 相似文献
2.
Efficient synthetic routes to gossyplure and its components (1a and 1b) were formulated. The three key units viz the alkynol 3, the bromide 5, and the alkanal 13 were derived from easily accessible starting materials. Alkylation of 3 with 5, and subsequent semihydrogenation followed by oxidation, provided the C11-alkenal 8 which was subjected to a stereocontrolled Wittig reaction with a C5-phosphonium salt, to yield directly the desired pheromone (1a + 1b). The synthesis of its individual components involved the manipulation via an acetylenic intermediate, viz the alkynol 14 which was obtained through alkylation of 3. A sequence of well-established reactions on 14, then provided the corresponding (E)- and (Z)-alkenylphosphonium salts which upon a (Z)-specific Wittig olefination with the C7-aldehyde (13), led to the stereoselective synthesis of 1a and 1b. 相似文献
3.
Dong Kyun You Ji Hye Lee Hyonseok Hwang Hyoshik Kwon Myung Hwan Park Kang Mun Lee 《Tetrahedron letters》2017,58(33):3246-3250
1,3,5-Tris-(o-carboranyl-methyl)benzene (closo-1) and its nido-form (nido-1) were synthesized and fully characterized. The solid-state molecular structure of closo-1 was determined by single-crystal X-ray diffraction analysis. Compound closo-1 exhibited an intense single emission in various organic solvents that was red-shifted with increasing solvent polarity. The positive solvatochromic effect and theoretical calculation results at the first excited (S1) optimized structure of closo-1 strongly suggest that this emissive band can be assigned to an intramolecular charge transfer. Meanwhile, nido-1 showed a pronounced red-shift of the emissive band compared to that of closo-1 and aroused low-energy emission. The specific emissive features of nido-1 were attributed to the elevation of its HOMO level, estimated by cyclic voltammetry. The photophysical changes by conversion from closo-1 to nido-1 allowed the emissive color-tunable sensing of fluoride. Thus, the tris-o-carboranyl compound showed great potential as a chemodosimeter for fluoride anion sensing, detectable by the naked-eye. 相似文献
4.
The structure of a new glucosidic iridoid, 6-epiaucubin 1, isolated from leaves of a tropical tree, Tecoma chrysantha Jacq., was established by analysis of the spectroscopical data of 1 and its hexa-O-acetyl derivative 3. Partial synthesis of 1 from its epimer, aucubin 2, is also reported. 相似文献
5.
《Tetrahedron: Asymmetry》1998,9(2):305-320
Methylcyclopropanone hemiacetal (2S)-3a underwent the asymmetric Strecker reaction induced by a chiral amine to provide a useful synthesis of enantiomerically pure (1R,2S)-(+)-allo-norcoronamic acid 1 in good yield and high enantiomeric excess. From racemic alkyl hemiacetal (±)-3, the same methodology also constituted a useful way to prepare both (+)-1 and (−)-1 and (+)-allo-coronamic acid 2 and its antipode (−)-2 with good yield and high enantiomeric excess. 相似文献
6.
《中国化学快报》2023,34(1):107469
Two chimeric sesterterpene synthases (AaTPS1 and AaTPS2) were functionally characterized from Alternaria alternata MB-30 isolated from the leaves of a sesterterpenoid-producing Lamiaceae plant Leucosceptrum canum. AaTPS1 generated a 5/8/6/5 tetracyclic sesteraltererol (1) and its absolute stereochemistry was determined by X-ray crystallographic analysis of its derivative 10,11-epoxysesteraltererol (2), which enabled revision of the absolute configuration of C7 of sesterfisherol produced by NfSS and PTTS014 characterized previously and its derivative 10,11-epoxysesterfisherol. AaTPS2 produced a 5/15 bicyclic preterpestacin I (3). Site-directed mutagenesis suggested that F192 in AaTPS1 was likely involved in controlling of the hydroxylation of C12, and eight amino acids were important for the enzyme activity of AaTPS1 and AaTPS2. The engineered Escherichia coli and Saccharomyces cerevisiae strains were constructed for the productions of compounds 1 and 3, and the highest titer of compound 1 reached 62.3 mg/L in shake-flask culture. Both compounds 1 and 2 showed anti-adipogenic activity. 相似文献
7.
《Tetrahedron: Asymmetry》2000,11(4):929-934
Pig liver esterase (PLE) was physically immobilised in a polysulphone ultrafiltration hollow fibre membrane reactor and used for the repetitive batch two-phase hydrolysis and separation, on a multigram scale, of the meso-diester dimethyl cis-cycloxex-4-ene-1,2-dicarboxylate 1 to enantiomerically pure (1S,2R)-cyclohex-4-ene-1,2-dicarboxylic acid monomethyl ester 2. After 25 days, the enzyme still retained its initial activity, which corresponds to 62% of its activity in the free form, and the enantiomeric purity of monoester 2 was still higher than 97%. Simple experimental conditions were established for the large laboratory scale preparation of substrate 1 and isolation of product 2 from the aqueous phase. 相似文献
8.
《Tetrahedron: Asymmetry》1998,9(7):1171-1178
The levorotatory enantiomer of t-butylsulfinylacetic acid 3 was obtained in the reaction of the α-carbanion of (+)-t-butyl methyl sulfoxide 1 with carbon dioxide. The same enantiopure form of the acid 3 was isolated from its diastereomerically pure levorotatory salt 5 with (−)-(1R,2S)-ephedrine. The structure of this salt was determined by X-ray analysis and the absolute configuration (S) at sulfur was ascribed to the t-butylsulfinylacetate anion. Consequently, the absolute configuration (S) was assigned to the acid (−)-3 and its precursor (+)-t-butyl methyl sulfoxide 1. 相似文献
9.
Gerhard Bringmann Dominik Hager Anu Schaumlöffel Matthias Groh Andreas Speicher 《Tetrahedron: Asymmetry》2013,24(9-10):575-581
Isoplagiochin C 1 was prepared for the first time in enantiopure form from synthetic racemic material, using a novel stereochemical concept. This macrocyclic bisbibenzyl contains two biaryl axes. Of these, axis A is configurationally stable by its fixation within the macrocyclic framework, while axis B is stereochemically unstable. By diesterification of rac-1 with enantiopure (P)-1,1′-binaphthyl-2,2′-dicarboxylic acid, axis B is locked in its P-configuration, thus allowing the resolution and separate saponification of dilactones (PA,PB,P)-3 and (MA,PB,P)-3 to give the pure enantiomers of 1. This concept permits recycling of any undesired enantiomer of 1 by thermal equilibration of the respective diastereomer of 3. 相似文献
10.
Hua-Dong Chen Yuan-Qing Ding Sheng-Ping Yang Xing-Cong Li Xu-Jie Wang Hai-Yan Zhang Daneel Ferreira Jian-Min Yue 《Tetrahedron》2012,68(30):6054-6058
Morusalbanol A (1), a neuro-protective Diels–Alder adduct with a new carbon skeleton, was isolated from the bark of Morus alba. Compound 1 showed evidence of interesting astropisomerism, and resulted in the absence of a number of key proton and carbon signals in the NMR spectra. Its structure was thus elucidated by spectroscopic analysis of its peracetylated derivative (2) and its absolute configuration established as 1S,3S,4R,5S via experimental and calculated ECD spectra of 1. In a neuro-protective assay, morusalbanol A (1) significantly attenuated the H2O2-induced cell damage in a dose-dependent manner. 相似文献
11.
threo-β-Hydroxy-l-glutamic acid 1 is an attractive target as a biologically active compound and as a chiral synthon. The required β-hydroxyl group in 1 was efficiently and stereoselectively introduced via an intramolecular conjugate addition of the N-hydroxymethyl group of γ-amino-α,β-unsaturated (Z)-ester 4. While the corresponding (E)-ester 3 gave a lower selectivity of ca. 5:1 in the intramolecular conjugate addition, a selectivity of up to 70:1 was shown with (Z)-ester 4. The tandem (Z)-olefination-conjugate addition could be achieved by simply changing the reaction conditions to give a selectivity of >20:1. Thus, the target compound 1 was obtained as its hydrochloride salt in 70% overall yield over four steps from lactol 2. 相似文献
12.
This paper summarizes our recent studies on the mechanism of O-atom transfer to a benzylic C–H bond promoted by dopamine β-hydroxylase (DBH) and its biomimetic models. We demonstrate that it is possible to carry out parallel and comparative studies on enzyme (DBH) and its biomimetic models with the same substrate: 2-aminoindane (1). It was chosen because its two stereogenic centers, both in benzylic positions, make it very powerful for studying the stereochemistry of an O-atom transfer reaction. DBH-catalyzed hydroxylation of 1 exclusively produced 14 % of trans-(1S,2S)-2-amino-1-indanol 4a (93 % e.e.). Studies with stereospecifically deuterium labeled 2-aminoindanes (1R,2S)-2 and (1S,2S)-3 showed that the formation of 4a was the result of an overall process with retention of configuration where an O-atom is stereospecifically inserted in the trans pro-S position of the substrate. Addition of 1 and (±)2 to 2-vinylpyridine gave 2-X-IndPY2 ligands 5 and 6, which were transformed into copper(I) and (II) complexes {7}(PF6) and {8}(CF3SO3), respectively. Reaction with dioxygen led to new complexes in which an O-atom transfer to a benzylic C–H bond has been performed in the same manner as that of DBH. With deuterium labeled cis-2-d-IndPY2 ligand 6, we demonstrated that the reaction occurs by a stereospecific process with retention of configuration. In both cases (enzymatic vs. biomimetic) the O-atom transfers occur in a two-step process involving radical intermediates. 相似文献
13.
Min Fan Yu Zhu Zhi-Jun Zhang Ru-Nan Du Qin-Feng Zhu Xing-De Wu Qin-Shi Zhao 《Tetrahedron letters》2018,59(2):143-146
A neo-clerodane diterpenoid, salvihispin A (1), as well as its glycoside, salvihispin A-2-O-β-d-3-keto-glucopyranoside (2) were isolated from the aerial parts of Salvia hispanica. Compound 2 possessed an unusual 3-keto-glucopyranoside moiety. Their structures and absolute configurations were elucidated by extensive spectroscopic methods and confirmed by single crystal X-ray diffraction. Salvihispin A (1) and its glycoside (2) enhanced the neurite outgrowth of NGF-mediated PC12 cells at a concentration of 10?μM. 相似文献
14.
《Tetrahedron: Asymmetry》2001,12(18):2551-2564
Enantiomerically pure (+)-(αR,α′R)-dimethylmesobilirubin-XIIIα 1 and its (αS,α′S) enantiomer ent-1 were synthesized in ten steps from simple precursors. Resolution was achieved at an early stage in the synthesis, with a racemic monopyrrole precursor rac-6 being converted to its amides 8 with (1S)-camphor-2,10-sultam. Resolution of 8 to 99% d.e. was accomplished in three crystallizations, and the absolute configuration of the acid 6 was deduced by X-ray crystallography of the more crystalline, diastereomerically pure amide 7. Circular dichroism spectroscopy of 1 showed intense bisignate Cotton effects: Δεmax435=+344, Δεmax391=−193 (CHCl3), as expected for a molecular exciton, and consistent with a P-helical intramolecularly hydrogen-bonded ridge-tile conformation. The Cotton effect magnitudes of 1 match almost exactly those found for (−)-(βS,β′S)-dimethylmesobilirubin-XIIIα 11 and (+)-(αR,β′R)-dimethylmesobilirubin-XIIIα. However, the Cotton effect of the pseudo-meso diastereomer (αR,β′S)-dimethylmesobilirubin-XIIIα 12 is not zero. Its large positive exciton couplet and 1H NMR NOE analysis confirm that an α-CH3 exerts a greater steric demand than a β-CH3—by a factor of ∼3. 相似文献
15.
A general method for the synthesis of the mitotic kinesin Eg5 inhibitor HR22C16 1 and its analogues based on protecting group (PG)-modulated highly diastereoselective Pictet–Spengler reaction of l-tryptophan methyl ester hydrochloride with meta-(RO)-benzaldehyde is described. By using the enantiomerically pure (1R,3S)-1,3-disubstituted tetrahydro-β-carboline trans-4c as a common chiral synthon, HR22C16 1 and its analogues 2 and 3 were synthesized in 90.1%, 90.2%, and 86.5% overall yields, respectively. 相似文献
16.
《Tetrahedron: Asymmetry》2014,25(18-19):1253-1263
Inversion at the highly congested C1 position of 1-epi-pathylactone A (1-epi-1), or its corresponding steroidal hybrid 8a, using a diverse range of published procedures including microwave assisted Mitsunobu reaction or via oxidation to the corresponding ketone and subsequent reduction, was unsuccessful in our hands. Attempts to convert the C1 hydroxyl group into its corresponding chloride, en route to napalilactone 2a, also failed. Precursors with the C1α configuration installed at early stage proved not to be amenable to the targets under a broad range of conditions. 相似文献
17.
Bromination of 6,6-diphenylfulvene 1 gives trans-trans-trans-1,2,3,4-tetrabromo-1,2,3,4-tetrahydro-6,6-diphenylfulvene 3 via trans-1,2-dibromo-1,2-dihydro-6,6-diphenylfulvene 2. Compound 3 in cyclohexane or carbon tetrachloride is converted by heating or exposure to sunlight to its trans-cis-trans stereoisomer 4. The structures of 3 and 4 have been established by X-ray crystallography. Compound 3 is converted to a third stereoisomer 5 on standing in chloroform or dichloromethane solution. Anomalies in the ultraviolet spectra of 3–5 can be interpreted in terms of an interaction of the π system with the bromine atoms at C(1) and C(4). The formation of addition products from 1 is indicative of its olefinic rather than aromatic character. 相似文献
18.
K. Mori 《Tetrahedron》1976,32(10):1101-1106
(S)-(?)-Ispenol 1′ and its antipode 1″ were synthesized from (S)-(+)-leucine 10 and its antipode 10′, respectively. This established the S-configuration of the naturally occurring (-)-ipsenol. Only the natural (S)-(?)-enantiomer was biologically active on Ips grandicollis. 相似文献
19.
《Tetrahedron: Asymmetry》1999,10(19):3747-3758
The PLE/MPEG catalyzed transesterification of the glycerol ketals rac-1a and rac-1d–f with vinyl propionate in toluene proceeded with good selectivities (E=24–34) and gave the enantiomerically enriched S-alcohols 1a and 1d–f, and the S-esters 2a and 2d–f. High selectivities (E=99 and E≥200) were observed in the transesterification of the glycerol ether rac-3 and its desoxy analog rac-5, both having a secondary hydroxy group, with PLE/MPEG. In transesterifications in organic media PLE exhibited a much higher enantioselectivity than in hydrolysis in water. 相似文献
20.
James M. Eagan Kyalo Stephen Kanyiva Masahiro Hori Scott A. Snyder 《Tetrahedron》2019,75(24):3145-3153
The synthesis of lindenatriene (1) and iso-lindenatriene (12) were achieved, along with the des-hydroxy model compounds (10 and 18, respectively), and compared to reported 1H NMR spectra in the literature (1a and 10a). These comparisons clarify the correct initial assignment of lindenatriene (1) as well as its instability and propensity to isomerize into the more thermodynamically favored iso-lindenatriene (12). 相似文献