The following oligosaccharide sequences containing the repeating unit of the O-specific chain of lipopolysaccharides from aeromonas salmonicida have been synthesized: α-D-Glcp-(1→3)-α-L-Rhap-(1 →3)-β-D-ManpNAcO(CH2)8CO2Me, α-D-Glcp-(1 →4)-α-D-Glcp-(1→3)-α-L-Rhap-(1→3)-β-D-ManpNAcO(CH2)8CO2Me and α-D-Glcp(1→4)-α-D-Glcp-(1→3)-[β-D-ManpNAc(1→4)]-L-Rha. 相似文献
A method for preparing haloconduritols having a conduritol-A construction is described. A mixture of endo- and exo-cycloadduct derivatives prepared from the Diels-Alder reaction of furan and vinylene carbonate was converted into diacetate derivatives by hydrolysis (K2CO3/MeOH) followed by acetylation (Ac2O/pyridine). Boron trihalide (BBr3 or BCl3)-assisted ring-opening of the endo-diacetate in CH2Cl2 at −78°C gave (1α,2α,3β,6β)-6-halogeno-4-cyclohexene-1,2,3-triol 1,2-diacetate from which the corresponding triacetate was prepared by acetylation (AcCl). trans-Esterification of the triacetate (MeOH/HCl) afforded (1α,2α,3β,6β)-6-halogeno-4-cyclohexene-1,2,3-triol (X=Br or Cl). BF3-Assisted ring-opening of the endo-diacetate in CH2Cl2 gave (1α,2α,3β,6β)-6-chloro-4-cyclohexene-1,2,3-triol 1,2-diacetate by means of halogen exchange. 相似文献
ABSTRACTN-glycosylation of 2,4-bis-O-(trimethylsilyl)-pyrimidine bases with 2-deoxy-2-fluoro-3,5-di-O-benzoyl-1-(Br, OBz)-α-d-arabinose derivatives are reported. 1-Bromo-arabinose provides high yield and a favorable anomeric ratio (β/α) of pyrimidine nucleoside in either MeCN or CH2Cl?CH2Cl. This method should be suitable for the synthesis of 2′-deoxy-2′-[18F]fluoro-1-β-d-arabinofuranosyluracil derivatives. 相似文献
all-L -β3-Penta-, hexa-, and heptapeptides with the proteinogenic side chains of valine, leucine, serine, cysteine, and methionine have been prepared by previously described procedures ( 12 , 13 , 14 , 15 ; Schemes 2 – 5). Thioether cleavage with Na/NH3 in β-HMet residues has also provided a β3-hexapeptide with homocysteine (CH2CH2S) side chains ( 13e ). The HS−(CH2)n groups were positioned on the β-peptidic backbone in such a way that, upon disulfide-bridge formation, the corresponding β-peptide was expected to maintain either a 31-helical secondary structure ( 1 , 2 ) (Fig. 1) or to be forced to adopt another conformation ( 3 , 4 ). The 13-, 17-, 19-, and 21-membered-ring macrocyclic disulfide derivatives and their open-chain precursors, as well as all synthetic intermediates, were purified (crystallization, flash or preparative HPL chromatography; Fig. 5) and fully characterized (m.p., [α]D, CD, IR, NMR, FAB or ESI mass spectroscopy, and elemental analysis, whenever possible; Fig. 2 and Exper. Part). The structures in MeOH and H2O of the new β-peptides were studied by CD spectroscopy (Figs. 3 and 4), where the characteristic 215-nm-trough/200-nm-peak pattern was used as an indicator for the presence or absence of (M)-31-helical conformations. A CH2−S2−CH2 and, somewhat less so, a (CH2)2−S2−(CH2)2 bracket between residues i and i+3 ( 1 vs. 12d , and 2 vs. 13e in Fig. 3) give rise to CD spectra which are compatible with the presence of 31-helical structures, while CH2−S2−CH2 brackets between residues i and i+2 ( 3 vs. 14c ) or i and i+4 ( 4 vs. 15c in Fig. 4) do not. 相似文献
The crystal and molecular structure of the complex Th[η5-(CH3)5C5]2[CH2-Si(CH3)3]2, which undergoes facile intramolecular cyclometalation to the thoracyclobutane Th[η5-(CH3)5C5]2(CH2)2Si(CH3)2, is reported. While the Th[η5-(CH3)5C5]2 ligation is unexceptional, the Th[CH2Si(CH3)3]2 fragment is highly unsymmetrical having Th-C (corresponding angle Th-C-Si) 2.51(1) Å (132.0(6)°) and 2.46(1) Å (148.0(7)°). This conformation, which appears to result from severe intramolecular non-bonded contacts, allows a methyl hydrogen atom of one CH2Si(CH3)3 ligand to approach within ca. 2.3 Å of the α-carbon atom of the other CH2Si(CH3)3 ligand. 相似文献
From the roots of oat (Avena sativa) a second antibiotic active glycoside, avenacine B, was isolated in addition to the main glycoside avenacine A. In the aglycone of A the double bond could not be established contrary to the statement in the literature but an aldehyde group in addition to the keto group was identified and therefore the proposed structure has to be revised. In the aglycone of B the —CH2OH-group of A has been substituted by CH3. The structures of the sugar chains in both glycosides have been determined, in avenacine A as [β-d-gluco-pyranosyl(1 → 4)-[β-d-glucopyranosyl (1 → 2)]-α-l-arabinosyl (1)- and in B as [β-d-glucopyranosyl (1 → 4)]-β-d-glucopyranosyl (1)-. 相似文献
Reaction of the Cage-like Silicic Acid Derivative [(CH3)2HSi]8Si8O20 with Unsaturated Organic Compounds By 29Si, 1H, and 13C NMR investigations were shown that the eight HSi?groups of the double four-ring silicic acid derivative [(CH3)2HSi]8Si8O20 react with the following unsaturated compounds: vinylcyclohexene, allyl glycidyl ether, methyl methacrylate, octadecene-1, and styrene. The resulting oily products are soluble in organic solvents. The compounds were characterized by the chemical shifts of the 29Si, 1H, and 13C NMR signals. Their formulae are [C6H9(CH2)2Si(CH3)2]8Si8O20, [CH3OOCCH(CH3)CH2Si(CH3)2]8Si8O20, [CH3(CH2)17Si(CH3)2]8Si8O20 and [C6H5(CH2)2Si(CH3)2]8Si8O20, and [C6H5CH(CH3)Si(CH3)2]8 Si8O20, respectively. Mainly the addition reactions do not follow the Markovnikov rule. 相似文献
A range of 4‐monosubstituted and 2,4‐disubstituted 1H‐imidazoles and 1H‐imidazole‐1‐ethanols (R C(4): CH2CH2Ph, CHOHCH2Ph, Ph, or Me; R C(2): CH2OH, CHOHCH2OH, CN, or CH2NHAc) were prepared and tested as inhibitors of α‐ and β‐glucosidases and of a β‐galactosidase. A new access to 4‐(2‐phenylethyl)‐1H‐imidazoles starting from 4‐phenylbutan‐1‐ol was elaborated. The strongest inhibitors are the 2‐substituted 4‐(2‐phenylethyl)‐1H‐imidazoles 24a and 26a (R C(2): CH2OH and CHOHCH2OH) and the 2‐phenylethanol 34 . They inhibit the β‐galactosidase from bovine liver and the β‐glucosidase from Caldocellum saccharolyticum with inhibition constants in the micromolar range, but do not inhibit the α‐glucosidase from brewer's yeast. 相似文献
To assess the importance of the phenol functionality in cannabinoids for analgetic activity a new series of 9-nor-9β-hydroxyhexahydrocannabinoids was prepared. The synthesis of 1-substituted (H, CH2OH, OH, NH2) 6aβ,7,8,9,10,10aα-hexahydro-9β-hydroxy-6,6-dimethyl-3-[1-methyl-4-phenylbutoxy]-6H-dibenzo[b,d]pyrans from 3,5-dihydroxystilbene, 3,3′,5,5′-tetrahydroxystilbene or 1,3,5-trihydroxybenzene is described. Relative stereochemistry and structure confirmations were obtained by nmr and X-ray crystal analysis. 相似文献
The synthesis of H-Pro-Leu-β-Ala-NH2, H-Pro-Leu-β-Ala-NHCH3 and H-Pro-Leu-β-Ala-N(CH3)2 is described. On the basis of IR and 1H NMR spectral data, a 7-membered ring including the NH of β-alanine with the CO of proline should be assigned for the H-Pro-Leu-β-Ala-N(CH3)2. Consequently, the plausible conformations for H-Pro-Leu-β-Ala-NH2 and H-Pro-Leu-β-Ala-NHCH3 derive from the formation of an 11-membered ring, between the trans amide proton and the CO of Pro, or from the formation of an 8-membered ring, between this carboxamide proton and the CO of Leu, plus the aforementioned 7-membered ring. 相似文献
Substituted phenyl iodides or diiodides reacted with ethyl iodotetrafluoroproponylate ICF2CF2CO2Et, 1 in the presence of copper powder to give the coupled products 2 or 3 in good yields. Addition of 1 to ethylene and allyl acetate proceeded smoothly under thermal and radical conditions to give the corresponding adducts, which underwent elimination reaction to give β-vinyl and β-allyl α,α,β,β-tetrafluoroesters, CH2CHCF2CF2CO2Et, 4 and CH2CHCH2CF2CF2CO2Et, 5, respectively. 1 also readily reacted with 1,5-hexadiene and 1-hexene with copper or palladium complex, followed by reduction to remove iodine to produce ω-alkenyl-α,α,β,β-tetrafluoroester CH2CH(CH2)4CF2CF2CO2Et 6 and α,α,β,β-tetrafluoroester C4H9CH2CHICF2CF2CO2Et. 相似文献
The infrared spectra of CH3CH2I, CD3CH2I, and CH3CD2I of the vapors and the solids at 170°C have been recorded from 4000-200 cm?1. The Raman spectra of the liquids and vapors have also been recorded and depolarization values have been measured. Assignment of the eighteen fundamental vibrations has been based on depolarization values, band contours, group-frequency correlations, and normal coordinate calculations. A critical discussion of the CH stretching assignments in CH3CH2X molecules is presented. 相似文献
Nucleosides and Nucleotides. Part 12. Synthesis of Dinucleoside Monophosphates Containing 1-(2′-Deoxy-β-D -ribofuranosyl)-2(1H)-pyrimidone The connexion of the modified nucleoside 1-(2′-deoxy-β-D -ribofuranosyl)-2(1H)-pyrimidone (Md, 2 ) with the natural nucleotides pTd and pGd is described. The protected dinucleoside monophosphates (MeOTr)MdpTd ( 6 ) and (MeOTr)MdpG ( 9 ) were prepared by the standard phosphodiester method using DCC as condensing agent. MdpTd ( 7 ) was obtained by treatment of 6 with formic acid/methanol 7 : 3 at 0° 9 was converted to the free dinucleoside monophosphate MdpGd ( 11 ) by removing the N-isobutyryl- and p-methoxytrityl protecting group on consecutive treatment with 0.04N CH3ONa in CH3OH and HCOOH/CH3OH 7:3 at 0° respectively. Enzymatic degradation of the free dinucleoside of the free dinucleoside monophosphates 7 and 11 yielded the corresponding nucleosides and nucleotides in the correct ratios. 相似文献
Cyclization of 2-carbomethoxy-3-(4',4'-dimethylcyclopent-2-enylmethyl)cyclopentanone (4) with N-phenylselenophthalimide and tin(IV) chloride affords cis-syn-cis-1β-carbomethoxy-4,4-dimethyl-3β-phenylselenotricyclo [6.3.0.02,6]undecan-11-one (8) and cis-anti-cis-1β-carbomethoxy-4,4-dimethyl-3α-phenylselenotricyclo [6.3.0.02,6]undecan-11-one (9). Both of these selenides can be elaborated to cis-anti-cis-4,4-dimethyl-1β-methyltricyclo [6.3.0.02,6]undecan-11-one (13) which upon treatment with CH2Br2/ TiCl4/Zn affords the sesquiterpene (±)-hirsutene (1) in 20% overall yield. 相似文献
Three water-soluble arsenic compounds were isolated from the green seaweed Codium fragile. These compounds were identified as 1-glycerophosphoryl-2-hydroxy-3-[5′-deoxy-5′-(dimethylarsinoyl)-β-ribofuranosyloxy]propane (1a), 1′ -(1,2-dihydroxypropyl)-5′ -deoxy-5′ -(dimethylarsinoyl)-β-ribofuranoside (1b), and dimethylarsinic acid ((CH3)2AsOOH). The structures of these compounds were ascertained by 1H NMR spectroscopy. Compounds 1a and 1b accounted for 60 % and dimethylarsinic acid for 5% of the water-soluble arsenic. 相似文献
We have observed the presence of vibrationally excited CH2- created in a discharge, by measuring the photodetachment from CH2- as it radiatively relaxes in a high vacuum ion trap. We used a tunable IR laser to produce photons with energies above and below the expected threshold for removing an electron from the ground state. The time dependence of the photodetachment is consistent with the electron affinity of 5250 cm-1 (0.65 eV) obtained by Sears and Bunker for the ground state X?3B1 methylene. We have tentatively assigned radiative lifetimes for the excited bending vibrations of CH2-:600 ±300 msec for v2 = 1,80±40msec for v2 = 2, and 10± 5 msec for v2 = 3. 相似文献
ABSTRACT The syntheses of α-D-GlcpNAc-(1→4)-β-D-Galp-(1→4)-β-D-GlcNAc-(1→O)-(CH2)15CH3 (1) and fragments thereof, corresponding to structures found in human ovarian cyst fluid, are described. Silver triflate promoted coupling of 3,4,6-tri-O-acetyl-2-azido-2-deoxy-β-D-glucopyranosyl bromide (12) and galactose acceptor (11) gave a disaccharide donor (13), which was readily transformed into the corresponding bromo-derivative 18. For the synthesis of disaccharide β-D-Galp-(1→4)-D-GlcNAc, several differently protected glucosamine acceptors were prepared. It was found that cetyl alcohol needed to be introduced after the formation of the β-galactoside bond. Glycosylation of pent-4-enyl 3,6-di-O-benzyl-2-deoxy-2-tetrachlorophthalimido-β-D-glucopyranoside (30) with (3,4,6-tri-O-acetyl-2-azido-2-deoxy-α-D-glucopyranosyl)-(1→4)-2,3,6-tri-O-benzoyl-α-D-galactopyranosyl bromide (18) by use of silver triflate as promoter gave the desired trisaccharide 31. Finally 31 was transformed via coupling to the long alkyl chain aglycon and deprotection into the title compound 1. 相似文献
A series of acyclic silyl diketonates, (CH3)3Si(dik), where dik = dipivaloyl-methanate, diisobutyrylmethanate and hexafluoroacetylacetonate, along with a new series of cyclic acetylacetonates of the type CH3(-CH2(CH2)xCH2-)Si(acac), where x = 1, 2, and 3, have been shown to possess enol ether structures in which the acyl group is positioned cis or trans to the silyl group. The ratios of cis to trans configurations in the (CH3)3Si(dik) series increase from <0.02 to >50.0 in the order of diketonate substituents CF3 < CH3 <i-C3H7 < t-C4H9. The ratios for the CH3(-CH2(CH2)xCH2-)Si(acac) compounds increases in the order χ = 1 > 2 > 3. These data are interpreted in terms of incipient pentacoordination of silicon by the carbonyl oxygen atom in the cis isomer. Rates of 1,5-migration of silicon between oxygen centers in the cis isomers have been determined by NMR spectroscopy. The dependence of the rearrangement rates on diketonate substituent and angle strain at silicon indicate that the migration process is better viewed as an internal nucleophilic displacement, rather than a sigmatropic shift. 1,5-Migration in the chiral (C6H5CH2)(CH3)(C6H5)Si derivative of dipivaloylmethanate occurs exclusively with retention of configuration at silicon. The large difference in activation energy for migration and inversion (>18 kcal/mol) precludes the possibility of distinguishing between a stepwise and concerted displacement mechanism. 相似文献
The mass spectra of some (Z)α-(4-R′-phenyl)-β-(2-thienyl-5-R)acrylonitriles (R = H, CH3, Br; R′ = H, CH3O, CH3, Cl, NO2) at 70 eV are reported. Mass spectra exhibit pronounced molecular ions. The compound's where R = H, and CH3 are characterized by the occurrence of a strong [M - H]+ peak. Moreover, in all the compounds a m/z 177 peak occurs. In the compounds where R = H, [M - HS]* and [M - CHS]* ions are present except the nitroderivatives. Where R = CH3, [M - HS]+ ion occurs. 相似文献
2-Butyne reacts stereospecifically with (PPh3)2Ni(Ph)(Br) in CH3OH at room temperature, leading to the isolable vinyl complex trans-(PPh3)2-Ni(Br)[cis-C(CH3)C(CH3)(Ph)] in 70% yield. Carbonylation (CO/CH3OH) of this material gives a 98% yield of cis-α,β-dimethylcinnamate. Reaction of the phenylnickel complex with 3-hexyne is more complicated; insertion again occurs, but the ultimate products of the reaction are phenyl-substituted styrenes and butadienes. Evidence is presented that free vinyl radicals are involved as intermediates in the 3-hexyne reaction. 相似文献