Synthesis of 14-Bromo and 14-Hydroxy Baccatin III Derviatives

Numerous efforts towards synthesis of anticancer drug paclitaxel (Taxol(r), 1a) with improved activities led to the modification at 13-phenylisoserine side chain and different positions of its core structure-baccatin III 1c1. At the same time, the activities of searching new taxoids for starting materials of new semi-synthetic paclitaxel analogs from Taxus spp. plant have not ever been stopped. Among these taxoids, 14?-hydroxy-10-deacetylbaccatin III 22 and 13-acetyl-9-dihydrobaccatin III …     

Biological Fingerprinting Analysis of Interaction Between Taxoids in Taxus and Microtubule Protein by Microdialysis Coupled with High-performance Liquid Chromatography/Mass Spectrometry for Screening Antimicrotubule Agents

Some natural products, such as traditional Chinese medicines（TCMs）, contain compounds with anticancer activity and have attracted a great interest in recent years as alternative anticancer therapies. A quick and convenient assay for screening antimicrotubule compounds in which in vitro microdialysis/high-performance liquid chromatography （HPLC） is used to monitor the binding of the compounds extracted from TCM Taxus cuspidata Siebold ＆ Zucc（Taxus） to microtubules is reported. It was observed that the extract of Taxus contains at least five compounds which have affinity interaction with microtubules by biological fingerprinting analysis, and they were identified as the taxoids of taxol, baccatin III, 10-deacetylbaccatin Ⅲ（10-DAB）, cephalomannine and 7-epi-10-deacetyltaxol （7-epi-10-DAT） based on the comparison of their high-performance liquid chromatographic/mass spectrometric and UV spectra with those of the standard samples, both assembly-promoting and disassembly-inhibiting characteristics of those compounds were evaluated. It was observed that baccatin Ⅲ and 10-DAB bound to microtubules and the binding degrees were influenced by GTP. Competitive binding behavior of taxol with other four taxoids to microtubules was also investigated.     

Screening for pharmaceutically important taxoids in Taxus baccata var. Aurea corr. with CC/SPE/HPLC-PDA procedure

Needles of 'the golden yew' Taxus baccata var. Aurea Corr. were extracted with methanol followed by pre-purification of the crude extract and column chromatographic (CC) separation on florisil in gradient mode (an increasing concentration of acetone in dichloromethane). The obtained fractions were concentrated and purified on silanized silica gel SPE cartridges and taxoids eluted with 75% methanol were analysed by HPLC-PDA procedure using Waters Symmetry C(18) column with gradient elution. The applied method enabled not only determination of four taxoids commonly occurring in yew extracts (10-deacetylbaccatin III, baccatin III, paclitaxel and cephalomannine), but also, on the basis of chromatographic behaviour and UV spectrum, 10-deacetylated taxoids (10-deacetylpaclitaxel, 10-deacetylcephalomannine, 7-xyloside-10-deacetylpaclitaxel and 10-deacetyltaxol C) could be detected together with 7-epi-10-deacetylpaclitaxel. From the needles of Taxus baccata var. Aurea Corr. the largest amounts isolated were of 10-deacetylbaccatin III, then 10-deacetylpaclitaxel and 7-xyloside-10-deacetylpaclitaxel, all compounds considered to be paclitaxel precursors in semisynthesis. The efficient mechanism of the separation of 10-acetylated taxoids from their 10-deacetylated derivatives on florisil on the basis of electron acceptor-electron donor interactions is discussed.     

Synthesis of a C(29)-C(51) subunit of spongistatin 1 (Altohyrtin A) starting from (R)-3-benzyloxy-2-methylpropan-1-ol

A protected C(29)-C(51) subunit ((+)-38) of spongistatin 1 has been obtained. Key steps involve the aldol condensation of (3S, 4R)-3-methyl-7-[(p-methoxybenzyl)oxy]-4-[(triethylsilyl)oxy]octan- 2-o ne ((-)-6) with (tert-butyl)dimethylsilyl 4-deoxy-2, 3-di-O-(methoxymethyl)-4-methyl-6-O-(tert-butyl)dimethylsilyl)-bet a-D -glycero-L-gluco-heptodialdo-1,5-pyranoside ((+)-7) and a C-glycosidation of (4R,7R&S,E)-7, 8-dichloro-2-methylidene-1-(trimethylsilyl)oct-5-en-4-yl p-methoxybenzoate (16). Aldehyde (+)-7 was derived from (R)-3-benzyloxy-2-methylpropan-1-ol ((+)-10) in 13 formal steps but requiring the isolation of five intermediate products only. The longest linear synthetic scheme converts (+)-10 into (+)-38 in 2% overall yield (isolation of 11 intermediate products).     

13C NMR investigation of solid-state polymorphism in 10-deacetyl baccatin III

To investigate the origins of solid-state NMR shift differences in polymorphs, carbon NMR chemical shift tensors are measured for two forms of solid 10-deacetyl baccatin III: a dimethyl sulfoxide (DMSO) solvate and an unsolvated form. A comparison of ab initio computed tensors that includes and omits the DMSO molecules demonstrates that lattice interactions cannot fully account for the shift differences in the two forms. Instead, conformational differences in the cyclohexenyl, benzoyl, and acetyl moieties are postulated to create the differences observed. X-ray analysis of six baccatin III analogues supports the suggested changes in the cyclohexenyl and benzoyl systems. The close statistical match of the (13)C chemical shifts of both polymorphic forms with those calculated using the X-ray geometry of 10-deacetyl baccatin III supports the contention that the B, C, and D rings are fairly rigid. Therefore, the observed tensor differences appear to arise primarily from conformational variations in ring substituents and the cyclohexenyl ring.     

Simultaneous determination of main taxoids in Taxus needles extracts by solid-phase extraction-high-performance liquid chromatography with pentafluorophenyl column

A simple and accurate RP-HPLC method with pentafluorophenyl (PFP) column was developed for the simultaneous determination of six taxoids, i.e. paclitaxel, 10-deacetylbaccatin III (10-DAB III), 7-xylosyl-10-deacetyltaxol (7-xyl-10-DAT), 10-deacetyltaxol (10-DAT), cephalomannine and 7-epi-10-deacetyltaxol (7-epi-10-DAT), in the extracts from the needles of three Taxus species. The mobile phase consisted of acetonitrile (A) and water (B), and the extracts were separated using gradient elution program: 30% A at the first 7 min, and then ramped to 42% A at 8 min, held until 38 min. The developed method was validated with satisfactory precision (RSD < 2.61%), repeatability (RSD < 2.92%) and recovery (95.19-104.47%). The above taxoids in the extracts of Taxus cuspidata, T. chinensis and T. media were analyzed with the developed RP-HPLC method, and the results showed that the contents of different taxoids in three mentioned species were distinct. Maximal amounts of 10-DAB III, 7-xyl-10-DAT and 7-epi-10-DAT appeared in T. chinensis, while T. media possessed the highest content of 10-DAT, cephalomannine and paclitaxel. The developed method is accurate and efficient. It can be reliably used in the improved determination of taxoids for the quality control of Taxus species.     

New bicyclic taxane diterpenoids from Taxus sumatrana

Investigation of an acetone extract of the leaves and twigs of Taxus sumatrana has resulted in the isolation of two new bicyclic taxoids, tasumatrols M (1), and N (2) and a new baccatin III derivative, tasumatrol O (3) together with the previous known 7-deacetylcanadensene (4) and 2alpha,7beta,13alpha-triacetoxy-5alpha,9alpha-dihydroxy-2(3-->20) abeotaxa-4(20),11-dien-10-one. The structures of these taxanes were established on the basis of spectroscopic analyses, especially 1- and 2D NMR, and chemical derivatization.     

Taxanes from the leaves of <Emphasis Type="Italic">Taxus cuspidata</Emphasis>

A new taxane, 13-oxobaccatin III (2), and five known taxanes, 10-deacetyl-13-oxobaccatin III (1), baccatin III (3), 7-epi-10-deacetyltaxol (4), 19-debenzoyl-19-acetyltaxinine M (5), and 5a-decinnamoyltaxagifine (6), were isolated from the leaves of the Japanese yew, Taxus cuspidate. Their structures were established on the basis of the analysis of their spectral data.     

New taxane derivatives: synthesis of baccatin[14,1-d]furan-2-one nucleus and its condensation with the norstatine side chain

New taxanes 15 and 18, containing the unsaturated and saturated baccatin[14,1-d]furan-2-one nucleus, respectively, were prepared starting from the readily available 13-oxo-7-Tes-baccatin III (3). Sequential formation of the enolate of 3 and reaction with ethyl glyoxylate gave the 13-oxo-7-Tes-baccatin[14,1-d]-3,4-dehydrofuran-2-one 4. The reduction of 4 can result in the formation of a mixture of compounds corresponding to 13-hydroxy alcohol 5 and 13-enol derivative 6. Both 5 and 6 were transformed into 13-oxo-7-Tes-baccatin[14,1-d]furan-2-one 8 by treatment with a base. Further reduction of 8 gave 13-hydroxy compound 9. Esterification of 6 and 9 with N,O-protected norstatine 12, followed by deprotection, gave the new promising anticancer taxanes 15 and 18, respectively.     

Synthesis of novel thiol surrogate of Taxol: 2′-deoxy-2′-mercaptopaclitaxel

Paclitaxel analogues with a thiol group in place of the hydroxyl group on the C-13 side chain constitute an interesting avenue of research for the study of new taxoid compounds. A synthetic route for the preparation of the exact thiol surrogate product of Taxol^® by coupling (4S, 5S)-2,4-diphenyloxazoline-5-carboxylic acid with 7-triethylsilyl baccatin III, followed by ring-opening of the oxazoline intermediate with thiolacetic acid is described.     

Rapid separation of four main taxoids in Taxus species by a combined LLP-SPE-HPLC (PAD) procedure

A method is described for the simultaneous determination of paclitaxel and three related taxoids, 10-deacetylbaccatin III (10-DAB III), baccatin III, and cephalomannine, in the extracts from the needles of three Chinese yew species, Taxus cuspidata, T. chinensis, and T. media. SPE was applied as the sample preparation technique and RP-HPLC with a photodiode array detector (PAD) was used for the analysis of extract samples. The crude extracts were treated with an improved SPE cartridge packed with a combination of 1-vinyl-pyrrolidin-2-one and divinyl-benzene. The eluent was 75% methanol. The following separation was achieved with a gradient program on an HIQ SIL C18W column in a system of ACN/water within 60 min. The samples were detected by PAD at wavelengths of 232.1 nm for 10-DAB III, 229.8 nm for baccatin III and paclitaxel, and 223.9 nm for cephalomannine. The content of 10-DAB III, baccatin III, cephalomannine, and paclitaxel varied from 0.0277 to 0.0875, 0.0254 to 0.0405, 0.0715 to 0.2486, and 0.0996 to 0.1301 mg/g in fresh needles of the above yew species, respectively. The assay achieved good resolution in the separation between the four compounds, and it can be used for quality control or purity determination for those in bulk and pharmceutical dosage forms.     

New labdane diterpenes from Solidago canadensis

The ethanol extract of roots of Solidago canadensis yielded eight labdane-type diterpenes. Five of those were new natural compounds (9,13,15,16-bisepoxy-labdane-7-ene-6,15-dione (3a), 13-epi-9,13,15,16-bisepoxy-labdane-7-ene-6,15-dione (3b), 15,16-epoxy-labdane-7,13-diene-6,16-dione (5), 15-ethoxy-9,13,15,16-bisepoxy-labdane-7-ene-6-one (6a) and 13-epi-15-ethoxy-9,13,15,16-bisepoxy-labdane-7-ene-6-one (6b). The known labdane diterpenes deoxysolidagenone (1), solidagenone (2) and 15,16-epoxy-labdane-7,13-diene-6,15-dione (4) were also isolated. Chemical structures were determined using 1D and 2D NMR techniques and MS analysis.     

13C?13C coupling constants in diacetylene (1,3-butadiyne) and its bis(triethylsilyl) derivative

Completely ¹³C-labelled diacetylene and its bis(triethylsilyl) derivative have been synthesized and all the possible spin–spin couplings between the acetylenic carbon nuclei have been determined from their Fourier transform ¹³C NMR spectra. J(CC) values in diacetylene have been also computed by means of the finite perturbation INDO method. Carbon–proton coupling constants in diacetylene have been determined from the spectrum at natural abundance. It has been established that J(CC) values across the triple bond in diacetylene and bis(triethylsilyl)diacetylene are greater than in acetylene and triethylsilylacetylene, respectively. The increase is interpreted in terms of σ- and π-electronic changes which occur with the coupling of two isolated triple bonds into a dimer-like system. All CC coupling constants are greater in diacetylene than in bis(triethylsilyl)diacetylene, which indicates that strong (p→d)π interaction takes place in the latter compound.     

Reactions of silylmercury compounds with sodium and potassium in the aromatic solvents

Bis(triethylsilyl)mercury (I) and triethylsilyl(pentaethyldisilanyl)mercury (II) react with metallic sodium or potassium in benzene solution to give phenyltriethylsilane (III) and a mixture of III and 1-phenyl-2,2,3,3,3-pentaethyldisilane, respectively, instead of the expected silylmetallic compounds (e.g. Et₃SiM and Et₅Si₂M, where M = Na or K). These results may be explained by the intermediate formation of silylmetallic compounds which reacted with the solvent. The reaction of I with potassium in toluene proceeds analogously.     

Activity Essential Residue Analysis of Taxoid 10β-O-Acetyl Transferase for Enzymatic Synthesis of Baccatin

Taxoid 10β-O-acetyl transferase (DBAT) is a key enzyme in the biosynthesis of the famous anticancer drug paclitaxel, which catalyses the formation of baccatin III from 10-deacetylbaccatin III (10-DAB). However, the activity essential residues of the enzyme are still unknown, and the acylation mechanism from its natural substrate 10-deacetylbaccatin III and acetyl CoA to baccatin III remains unclear. In this study, the homology modelling, molecular docking, site-directed mutagenesis, and kinetic parameter determination of the enzyme were carried out. The results showed that the enzyme mutant DBAT^H162A resulted in complete loss of enzymatic activity, suggesting that the residue histidine at 162 was essential to DBAT activity. Residues D166 and R363 which were located in the pocket of the enzyme by homology modelling and molecular docking were also important for DBAT activity through the site-directed mutations. Furthermore, four amino acid residues including S31 and D34 from motif SXXD, D372 and G376 from motif DFGWG also played important roles on acylation. This was the first report of the elucidation of the activity essential residues of DBAT, making it possible for the further structural-based re-design of the enzyme for efficient biotransformation of baccatin III and paclitaxel.     

传统中药甘遂根中二萜类化学成分的电喷雾质谱研究

应用电喷雾多级串联质谱技术对传统中药甘遂根中的弱极性部分化学成分进行了分析鉴定, 根据串联质谱数据, 共鉴定出39个化合物. 其中包括9个新化合物: 分别为3-O-(2,3-二甲基丁酰基)-13,20-O-双十二烷酰基巨大戟萜醇(1)、3-O-(2,3-二甲基丁酰基)-13-O-癸酰基-20-O-十六烷酰基巨大戟萜醇(2)、3-O-(2,3-二甲基丁酰基)-13-O-十二烷酰基-20-O-[(9Z,12Z)-十八烷-9,12-二烯酰基]巨大戟萜醇(3)、3-O-(2,3-二甲基丁酰基)-13-O-十二烷酰基-20-O-(十八烷-9Z-烯酰基)巨大戟萜醇(4)、甘遂素I(5)、甘遂素J(6)、甘遂素K(7)、甘遂素L(8)和甘遂素M(9).     

Synthesis and antitumor activity of 2-(m-substituted-benzoyl)baccatin III analogs from taxinine

2-m-Azidobenzoyl and 2-m-chlorobenzoyl baccatin III analogs were prepared from taxinine, a major component in Japanese yew leaves. In this study, a novel acetyl migration from 13- to 4-hydroxyl group was observed. The antitumor activity of these compounds was evaluated.     

Vibrational circular dichroism analysis reveals a conformational change of the baccatin III ring of paclitaxel: visualization of conformations using a new code for structure-activity relationships

The comparison between measured and conformer-weighted calculated VCD spectra of the baccatin III ring of paclitaxel and visualization of the conformations using the new code for structure-activity relationships are reported for the first time. The VCD spectrum of paclitaxel closely resembles that of the baccatin III ring. The large characteristic nuCO VCD bands with bisignate signs (1732 cm-1, Deltaepsilon = -1.6 x 10(-1); 1715 cm(-1), Deltaepsilon = 2.4 x 10(-1)) strongly reflect the structural property of the family of conformations bacc-ABC32F defined using the new code. The comparison with the conformation of the baccatin III core in the electron micrograph of the crystal structure of tubulin-paclitaxel (1JFF) suggests a conformational change of paclitaxel corresponding to a switch through the binding with beta-tublin and the intermolecular interactions involving the hydroxyl group (D) and carbonyl of acetoxy group (E). The representation of conformational codes allows complicated conformations to be very easily compared and facilitates future computational analyses such as those for the large-molecule calculations as well as genome analysis.     

A New Taxoid from Leaves and Branches of Taxus chinensis

A new taxoid, 2-deacetyl-2α, 14β-dihydroxybaccatin Ⅳ (1), was isolated from the leaves and branches of Taxus chinensis together with the known compound baccatin Ⅳ (2). The structure of the new compound was elucidated by spectroscopic techniques. The detailed ^13C NMR assignments of baccatin Ⅳ are reported for the first time.