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1.
Amide hydrogen exchange coupled to nano‐electrospray ionization mass spectrometry (nano‐ESI‐MS) has been used to identify and characterize localized conformational changes of Akt upon activation. Active or inactive Akt was incubated in D2O buffer, digested with pepsin, and analyzed by nano‐ESI‐MS to determine the deuterium incorporation. The hydrogen/deuterium (H/D) exchange profiles revealed that Akt undergoes considerable conformational changes in the core structures of all three individual domains after activation. In the PH domain, four β‐strand (β1, β2 β5 and β6) regions containing membrane‐binding residues displayed higher solvent accessibility in the inactive state, suggesting that the PH domain is readily available for the binding to the plasma membrane for activation. In contrast, these β‐strands became less exposed or more folded in the active form, which is favored for the dissociation of Akt from the membrane. The beginning α‐helix J region and the C‐terminal locus (T450‐470P) of the regulatory domain showed less folded structures that probably enable substrate entry. Our data also revealed detailed conformational changes of Akt in the kinase domain due to activation, some of which may be attributed to the interaction of the basic residues with phosphorylation sites. Our H/D exchange results indicating the conformational status of Akt at different activation states provided new insight for the regulation of this critical protein involved in cell survival. Published in 2009 by John Wiley & Sons, Ltd.  相似文献   

2.
The structural stability of cyclophilin A (CypA) was investigated using H/D exchange and temperature coefficients of chemical shifts of amide protons, monitored by 213 heteronuclear NMR spectroscopy. Amide proton exchange rates were measured by H/D exchange experiments for slow-exchange protons and measured by SEA (Solvent Exposed Amides)-HSQC experiments for fast-exchange protons. Temperature coefficients of chemical shifts and hydrogen exchange rates of amide protons show reasonably good correlation with the protein structure. Totally, 44 out of 153 non-proline assigned residues still exist in 86 d of hydrogen-deuterium exchange at 4 ℃, suggesting that CypA structure should be highly stable. Residues in secondary structures of α2, β1, β2, β5, β6 and β7 might constitute the hydrophobic core of the protein. The change in free energy of unfolding ( △Gu^H2O ) of CypA was estimated to be (21.99± 1.53) kJ·mol^-1 by circular dichroism (CD). The large free energy change is also an indicator of the high structural stability.  相似文献   

3.
For the convenient synthesis of (1→6)‐α‐D ‐glucopyranan, i. e., dextran ( 4 ), ring‐opening polymerization of 1,6‐anhydro‐2,3,4‐tri‐O‐allyl‐β‐D ‐glucopyranose ( 1 ) has been carried out using BF3·OEt2. With a ratio of [BF3·OEt2]/[ 1 ] = 0.5 at 0 °C for 140 h, the yield and Mn of the obtained polymer are 84.0% and 21 700, respectively. The polymer consists of (1→6)‐α‐linked 2,3,4‐tri‐O‐allyl‐D ‐glucopyranose ( 2 ) which is similar to the results for the cationic ring‐opening polymerization of 1,6‐anhydro‐2,3,4‐tri‐O‐methyl‐β‐D ‐glucopyranose and 1,6‐anhydro‐2,3,4‐tri‐O‐ethyl‐β‐D ‐glucopyranose. Polymer 2 was isomerized using tris(triphenylphosphine)‐chlororhodium as the catalyst in toluene/ethanol/water to yield polymeric 2,3,4‐tri‐O‐propenyl‐(1→6)‐α‐D ‐glucopyranan ( 3 ). Deprotection of the propenyl ether linkage of 3 was then performed using hydrochloric acid in acetone to give 4 .  相似文献   

4.
The 4‐quinolones having the urea or carbamate moiety at the 2‐position showed the facile deuterium–hydrogen (D–H) exchange of the 3‐H proton in deuteriotrifluoroacetic acid‐deuteriodimethyl sulfoxide (3:1) at 60°C, whereas the 4‐quinolones possessing the carboxylate or carbohydrazide group at the 2‐position and 2‐substituted 4‐methoxyquinolines represented no D –H exchange of the 3‐H proton under the same condition. The aforementioned D–H exchange was found to require both the tautomerization of the 4‐quinolone into 4‐hydroxyquinoline in strongly acidic media and the nitrogen functional group at the 2‐position.  相似文献   

5.
Four new 9,10‐secocycloartane (=9,19‐cyclo‐9,10‐secolanostane) triterpenoidal saponins, named huangqiyenins G–J ( 1 – 4 , resp.), were isolated from Astragalus membranaceus Bunge leaves. The acid hydrolysis of 1 – 4 with 1M aqueous HCl yielded D ‐glucose, which was identified by GC analysis after treatment with L ‐cysteine methyl ester hydrochloride. The structures of 1 – 4 were established by detailed spectroscopic analysis as (3β,6α,10α,16β,24E)‐3,6‐bis(acetyloxy)‐10,16‐dihydroxy‐12‐oxo‐9,19‐cyclo‐9,10‐secolanosta‐9(11),24‐dien‐26‐yl β‐D ‐glucopyranoside ( 1 ), (3β,6a,10α,24E)‐3,6‐bis(acetyloxy)‐10‐hydroxy‐12,16‐dioxo‐9,19‐cyclo‐9,10‐secolanosta‐9(11),24‐dien‐26‐yl β‐D ‐glucopyranoside ( 2 ), (3β,6α,9α,10α,16β,24E)‐3,6‐bis(acetyloxy)‐9,10,16‐trihydroxy‐9,19‐cyclo‐9,10‐secolanosta‐11,24‐dien‐26‐yl β‐D ‐glucopyranoside ( 3 ), and (3β,6α,10α,24E)‐3,6‐bis(acetyloxy)‐10‐hydroxy‐16‐oxo‐9,19‐cyclo‐9,10‐secolanosta‐9(11),24‐dien‐26‐yl β‐D ‐glucopyranoside ( 4 ).  相似文献   

6.
The base‐pairing properties of oligonucleotides containing the anomeric 5‐aza‐7‐deazaguanine 2′‐deoxyribonucleosides 1 and 5 are described. The oligonucleotides were prepared by solid‐phase synthesis, employing phosphoramidite or phosphonate chemistry. Stable `purine'⋅purine duplexes with antiparallel (aps) chain orientation are formed, when the α‐D ‐anomer 5 alternates with the β‐D ‐anomeric 2′‐deoxyguanosine ( 2 ) within the same oligonucleotide chain. Parallel (ps) oligonucleotide duplexes are observed, when the β‐D anomer 1 alternates with 2 . A renewed reversal of the chain orientation (ps→aps) occurs when compound 1 pairs with 2′‐deoxyisoguanosine ( 6 ). In all cases, it is unnecessary to change the orientation within a single strand when α‐D units alternate with their β‐D counterparts. Heterochiral base pairs of 5 (α‐D ) with 2′‐deoxyisoguanosine (β‐D ) are well accommodated in duplexes with random base composition and parallel chain orientation. Base pairs of 5 (α‐D ) with 2′‐deoxyguanosine (β‐D ) destabilize duplexes with antiparallel chains.  相似文献   

7.
Addition reactions of acid chlorides with various 2‐substituted 4,5‐dihydro‐4,4‐dimethyl‐5‐(methylsulfanyl)‐1,3‐thiazoles under basic conditions were studied. Two kinds of products were obtained from these additions, β‐lactams and non‐β‐lactam adducts. When the reaction was carried out with 4,5‐dihydro‐1,3‐thiazoles with a Ph substituent at C(2), the reaction proceeded via formal [2+2] cycloaddition and led to the correspoding β‐lactam. On the other hand, acid chlorides and 4,5‐dihydro‐1,3‐thiazoles bearing an α‐H‐atom at the C(2)‐substituent underwent C(α)‐ and/or N‐addition reactions and furnished non‐β‐lactam adducts, i.e., C(α)‐ and/or N‐acylated 1,3‐thiazolidines. The attempted transformations of sulfonyl esters of exo‐6‐hydroxy penams to endo‐6‐azido penams failed, although they were successful with mono‐β‐lactams under the same conditions.  相似文献   

8.
Two new saponins were isolated from husks of Xanthoceras sorbifolia Bunge and their structures were elucidated as 3‐O‐[β‐D‐galactopyranosyl(1→2)]‐α‐L‐arabinofuranosyl(1→3)‐β‐D‐methyl glucuronic acid‐21‐O‐(3,4‐diangeloyl)‐α‐L‐rhamnose‐3β, 16α, 21β, 22α, 28β‐pentahydroxyl‐22‐acetoxy‐olean‐12‐ene(1) and 3‐O‐[β‐D‐galactopyranosyl(1→2)]‐α‐L‐arabinofuranosyl(1→3)‐β‐D‐methyl glucuronic acid‐21,22‐O‐diangeloyl‐3β,15α,16α,21β,22α,28β‐hexahydroxyl‐olean‐12‐ene(2) on the basis of 1D and 2D NMR (including 1H, 13C‐NMR, 1H? 1H COSY, HSQC, HMBC and DEPT), ESI‐MS spectrometry and chemical methods. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

9.
Kaempferol 3‐Oβ‐glucopyranoside, kaempferol 3‐Oβ‐galactopyranoside and higher glycosides of these two flavonoids with α‐rhamnose at C‐2 and/or C‐6 of the primary sugar were studied by negative ion electrospray ionisation and serial mass spectrometry in a three‐dimensional (3D) ion trap mass spectrometer. Kaempferol 3‐Oβ‐glucopyranoside and kaempferol 3‐Oα‐rhamnopyranosyl(1→6)‐β‐glucopyranoside could be distinguished from their respective galactose analogues by differences in the ratio of the radical aglycone ion [Y0 – H]?? to the rearrangement aglycone ion Y following MS/MS of the deprotonated molecules. Kaempferol 3‐O‐rhamnopyranosyl(1→2)‐β‐glucopyranoside and kaempferol 3‐Oα‐rhamnopyranosyl(1→2)[α‐rhamnopyranosyl(1→6)]‐β‐glucopyranoside could be distinguished from their respective galactose analogues by differences in the product ion spectra of the [(M – H) – rhamnose]? ion following serial mass spectrometry. In the triglycoside, it was deduced that this ion resulted from the loss of the rhamnose substituted at 2‐OH of the primary sugar by observing that MS/MS of deprotonated kaempferol 3‐Oβ‐glucopyranosyl(1→2)[α‐rhamnopyranosyl(1→6)]‐β‐glucopyranoside showed the loss of glucose and not rhamnose. Thus the class of sugar (hexose, deoxyhexose, pentose) at C‐2 and C‐6 of the primary sugar can be determined. These observations aid the assignment of kaempferol 3‐O‐glycosides, having glucose or galactose as the primary glycosidic sugar, in LC/MS analyses of plant extracts, and this can be done with reference to only a few standards. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

10.
A new type of isocoumarins (=1H‐isochromen‐1‐ones=1H‐2‐benzopyran‐1‐ones), 4‐substituted 3,4‐dihydro‐3‐methoxyisocoumarins 2 , can be obtained by a one‐pot process from α‐substituted 2‐bromo‐β‐methoxystyrenes 1 . Thus, lithium 2‐(1‐aryl(or methyl)‐2‐methoxyethenyl)benzoates are conveniently generated via the Br/Li exchange between 1 and BuLi, followed by the action of CO2 on the resulting α‐substituted 2‐lithio‐β‐methoxystyrenes. Upon treating with concentrated HCl at room temperature, these lithium benzoates undergo lactonization to provide the desired 3,4‐dihydroisocoumarins 2 in relatively good yields.  相似文献   

11.
Five novel pyrazole‐coupled glucosides, 1,5‐diaryl‐1H‐pyrazol‐3‐yl 2,3,4,6‐tetra‐O‐acetyl‐β‐D ‐glucopyranosides 5a – 5e , were synthesized by the phase‐transfer catalytic reaction of 1,5‐diaryl‐1H‐pyrazol‐3‐ols 4a – 4e with acetobromo‐α‐D ‐glucose in H2O/CHCl3 under alkaline conditions, using Bu4N+Br? as catalyst. Then, glucosides 5a – 5c were deacetylated in a solution of Na2CO3/MeOH to yield the 1,5‐diaryl‐3‐(β‐D ‐glucopyranosyloxy)‐1H‐pyrazoles 6a – 6c . Their structures were characterized by 1H,1H‐COSY, 1H‐, 13C‐, and 19F‐NMR spectroscopy, as well as elemental analysis. The structures of 5d and 6c were also determined by single‐crystal X‐ray diffraction analysis. A preliminary in vitro bioassay indicated that compounds 4e and 5d exhibited excellent‐to‐medium fungicidal activity against Sclerotinia sclerotiorum at the dosage of 10 μg/ml.  相似文献   

12.
The 1,3,4,6‐tetra‐O‐acetyl‐2‐azido‐2‐deoxy‐β‐D ‐mannopyranose ( 4 ) or the mixture of 1,3,6‐tri‐O‐acetyl‐2‐azido‐2‐deoxy‐4‐O‐(2,3,4,6‐tetra‐O‐acetyl‐β‐D ‐galactopyranosyl)‐β‐D ‐mannopyranose ( 10 ) and the corresponding α‐D ‐glucopyranose‐type glycosyl donor 9 / 10 reacted at room temperature with protected nucleosides 12 – 15 in CH2Cl2 solution in the presence of BF3?OEt2 as promoter to give 5′‐O‐(2‐azido‐2‐deoxy‐α‐D ‐glycosyl)nucleosides in reasonable yields (Schemes 2 and 3). Only the 5′‐O‐(α‐D ‐mannopyranosyl)nucleosides were obtained. Compounds 21, 28, 30 , and 31 showed growth inhibition of HeLa cells and hepatoma Bel‐7402 cells at a concentration of 10 μM in vitro.  相似文献   

13.
Three new dammarane‐type triterpenoid saponins, 1 – 3 , were isolated and identified as (20S)‐20‐O‐[β‐D ‐xylopyranosyl‐(1→6)‐β‐D ‐glucopyranosyl‐(1→6)‐β‐D ‐glucopyranosyl]dammar‐24‐ene‐3β,6α,12β, 20‐tetrol ( 1 ), (20S)‐6‐O‐[(E)‐but‐2‐enoyl‐(1→6)‐β‐D ‐glucopyranosyl]dammar‐24‐ene‐3β,6α,12β,20‐tetrol ( 2 ), and (20S)‐6‐O‐[β‐D ‐xylopyranosyl‐(1→2)‐β‐D ‐xylopyranosyl]dammar‐24‐ene‐3β,6α,12β,20‐tetrol ( 3 ) from the roots of Panax notoginseng (Burkill ) F.H.Chen (Araliaceae). Their structures were elucidated on the basis of spectroscopic analyses, including 1D‐ and 2D‐NMR techniques and HR‐ESI‐MS, as well as by acidic hydrolysis.  相似文献   

14.
Seventeen flavonoids, five of which are flavone C‐diosides, 1 – 5 , were isolated from the BuOH‐ and AcOEt‐soluble fractions of the leaf extract of Machilus konishii. Among 1 – 5 , apigenin 6‐Cβ‐D ‐xylopyranosyl‐2″‐Oβ‐D ‐glucopyranoside ( 2 ), apigenin 8‐Cα‐L ‐arabinopyranosyl‐2″‐Oβ‐D ‐glucopyranoside ( 4 ), and apigenin 8‐Cβ‐D ‐xylopyranosyl‐2″‐Oβ‐D ‐glucopyranoside ( 5 ) are new. Both 4 and 5 are present as rotamer pairs. The structures of the new compounds were elucidated on the basis of NMR‐spectroscopic analyses and MS data. In addition, the 1H‐ and 13C‐NMR data of apigenin 6‐Cα‐L ‐arabinopyranosyl‐2″‐Oβ‐D ‐glucopyranoside ( 3 ) were assigned for the first time. The isolated compounds were assayed against α‐glucosidase (type IV from Bacillus stearothermophilus). Kaempferol 3‐O‐(2‐β‐D ‐apiofuranosyl)‐α‐L ‐rhamnopyranoside ( 12 ) was found to possess the best inhibitory activity with an IC50 value of 29.3 μM .  相似文献   

15.
New syntheses of C(2′)‐deuterated ribonucleosides have been accomplished starting either from 3,5‐di‐O‐benzyl‐1‐O‐methyl‐α,β‐D ‐ribofuranose ( 1b ) or 2,3‐O‐isopropylidene‐D ‐ribose ( 14 ), with >97 atom‐% D incorporation in both cases. The former is suited to the demands of multiple‐site deuteration or uniform 13C/multiple 2H double labeling of the ribofuranose moiety, whereas the latter is particularly appropriate for single‐site 2H labeling for mechanistic studies of enzyme reactions.  相似文献   

16.
Iodination of N2‐isobutyryl‐5‐aza‐7‐deazaguanine ( 7 ) with N‐iodosuccinimide (NIS) gave 7‐iodo‐N2‐isobutyryl‐5‐aza‐7‐deazaguanine ( 8 ) in a regioselective reaction (Scheme 1). Nucleobase‐anion glycosylation of 8 with 2‐deoxy‐3,5‐di‐O‐toluoyl‐α‐D ‐ or α‐L ‐erythro‐pentofuranosyl chloride furnished anomeric mixtures of D ‐ and L ‐nucleosides. The anomeric D ‐nucleosides were separated by crystallization to give the α‐D ‐anomer and β‐D ‐anomer with excellent optical purity. Deprotection gave the 7‐iodo‐5‐aza‐7‐deazaguanine 2′‐deoxyribonucleosides 3 (β‐D ; ≥99% de) and 4 (α‐D ; ≥99% de). The reaction sequence performed with the D ‐series was also applied to L ‐nucleosides to furnish compounds 5 (β‐L ; ≥99% de) and 6 (α‐L ; ≥95% de).  相似文献   

17.
The Oshima? Nozaki (Et2AlI) condensation of isolevoglucosenone ( 4 ) with 2,6‐anhydro‐3,4,5,7‐tetra‐O‐benzyl‐D ‐glycero‐D ‐gulo‐heptose ( 5 ) gave an enone 6 that was converted with high stereoselectivity to 3‐C‐[(1R)‐2,6‐anhydro‐D ‐glycero‐D ‐gulo‐heptitol‐1‐C‐yl]‐2,3‐dideoxy‐D ‐arabino‐hexose ( 1 ; 1 : 1 mixture of α‐ and β‐D ‐pyranose), and to 3‐C‐[(1R)‐2,6‐anhydro‐D ‐glycero‐D ‐gulo‐heptitol‐1‐C‐yl]‐2,3‐dideoxy‐D ‐lyxo‐hexose ( 2 ; 2.7 : 1.4 : 1.0 : 1.4 mixture of α‐D ‐furanose, β‐D ‐furanose, α‐D ‐pyranose, and β‐D ‐pyranose). The Oshima? Nozaki (Et2AlI) condensation of levoglucosenone ( 17 ) with aldehyde 5 gave an enone 18 that was converted with high stereoselectivity to 3‐C‐[(1R)‐2,6‐anhydro‐D ‐glycero‐D ‐gulo‐heptitol‐1‐C‐yl]‐3,4‐dideoxy‐α‐D ‐arabino‐hexopyranose ( 3 ; single anomer).  相似文献   

18.
Starting from methyl 2,3‐O‐isopropylidene‐α‐D ‐mannofuranoside ( 5 ), methyl 6‐O‐benzyl‐2,3‐O‐isopropylidene‐α‐D ‐lyxo‐hexofuranosid‐5‐ulose ( 12 ) was prepared in three steps. The addition reaction of dimethyl phosphonate to 12 , followed by deoxygenation of 5‐OH group, provided the 5‐deoxy‐5‐dimethoxyphosphinyl‐α‐D ‐mannofuranoside derivative 15a and the β‐L ‐gulofuranoside isomer 15b . Reduction of 15a and 15b with sodium dihydrobis(2‐methoxyethoxy)aluminate, followed by the action of HCl and then H2O2, afforded the D ‐mannopyranose ( 17 ) and L ‐gulopyranose analog 21 , each having a phosphinyl group in the hemiacetal ring. These were converted to the corresponding 1,2,3,4,6‐penta‐O‐acetyl‐5‐methoxyphosphinyl derivatives 19 and 23 , respectively, structures and conformations (4C1 or 1C4, resp.) of which were established by 1H‐NMR spectroscopy.  相似文献   

19.
Two new homo‐aro‐cholestane glycosides and a new cholestane glycoside, along with three known saponins, were isolated from the 95% EtOH extract of the roots and rhizomes of Paris polyphylla var. pseudothibetica. The structures of the new compounds were elucidated as 3βO‐{α‐L ‐rhamnopyranosyl‐(1→4)‐α‐L ‐rhamnopyranosyl‐(1→4)‐[α‐L ‐rhamnopyranosyl‐(1→2)]}‐β‐D ‐glucopyranosylhomo‐aro‐cholest‐5‐ene‐26‐Oβ‐D ‐glucopyranoside (parispseudoside A, 1 ), 3βOα‐L ‐rhamnopyranosyl‐(1→2)‐β‐D ‐glucopyranosylhomo‐aro‐cholest‐5‐ene‐26‐Oβ‐D ‐glucopyranoside (parispseudoside B, 2 ), and (25R)‐3βO‐{α‐L ‐rhamnopyranosyl‐(1→4)‐α‐L ‐rhamnopyranosyl‐(1→4)‐[α‐L ‐rhamnopyranosyl‐(1→2)]}‐β‐D ‐glucopyranosyl‐cholesta‐5,17(20)‐diene‐16,22‐dione‐26‐Oβ‐D ‐glucopyranoside (parispseudoside C, 3 ) by spectroscopic methods, including 1D‐ and 2D‐NMR, and MS experiments, as well as chemical evidences.  相似文献   

20.
Four new furostanol steroid saponins, borivilianosides A–D ( 1 – 4 , resp.), corresponding to (3β,5α,22R,25R)‐26‐(β‐D ‐glucopyranosyloxy)‐22‐hydroxyfurostan‐3‐yl Oβ‐D ‐xylopyranosyl‐(1→3)‐Oβ‐D ‐glucopyranosyl‐(1→4)‐O‐[α‐L ‐rhamnopyranosyl‐(1→2)]‐β‐D ‐galactopyranoside ( 1 ), (3β,5α,22R,25R)‐ 26‐(β‐D ‐glucopyranosyloxy)‐22‐methoxyfurostan‐3‐yl Oβ‐D ‐xylopyranosyl‐(1→3)‐Oβ‐D ‐glucopyranosyl‐(1→4)‐O‐[α‐L ‐rhamnopyranosyl‐(1→2)]‐β‐D ‐galactopyranoside ( 2 ), (3β,5α,22R,25R)‐26‐(β‐D ‐glucopyranosyloxy)‐22‐methoxyfurostan‐3‐yl Oβ‐D ‐xylopyranosyl‐(1→3)‐O‐[β‐D ‐glucopyranosyl‐(1→2)]‐Oβ‐D ‐glucopyranosyl‐(1→4)‐β‐D ‐galactopyranoside ( 3 ), and (3β,5α,25R)‐26‐(β‐D ‐glucopyranosyloxy)furost‐20(22)‐en‐3‐yl Oβ‐D ‐xylopyranosyl‐(1→3)‐O‐[β‐D ‐glucopyranosyl‐(1→2)]‐Oβ‐D ‐glucopyranosyl‐(1→4)‐β‐D ‐galactopyranoside ( 4 ), together with the known tribuluside A and (3β,5α,22R,25R)‐26‐(β‐D ‐glucopyranosyloxy)‐22‐methoxyfurostan‐3‐yl Oβ‐D ‐xylopyranosyl‐(1→2)‐O‐[β‐D ‐xylopyranosyl‐(1→3)]‐Oβ‐D ‐glucopyranosyl‐(1→4)‐O‐[α‐L ‐rhamnopyranosyl‐(1→2)]‐β‐D ‐galactopyranoside were isolated from the dried roots of Chlorophytum borivilianum Sant and Fern . Their structures were elucidated by 2D ‐NMR analyses (COSY, TOCSY, NOESY, HSQC, and HMBC) and mass spectrometry.  相似文献   

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