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61.
Max Herberhold Udo Drfler Bemd Wrackmeyer 《Journal of organometallic chemistry》1997,530(1-2):117-120
1,2-Bis(dimethylamino)-1,2-dibora-[2]ferrocenophane (1) was prepared by the reaction of 1,1′-dilithioferrocene with 1,2-dichlorobis(dimethylamino)diborane(4). In addition to hindered rotation about the B-N bond (ΔG‡ > 80 kJ mol−1), another dynamic process was revealed by 1H and 13C NMR in solution at low temperature, and interpreted as motion of the cyclopentadienyl rings between staggered and eclipsed conformations (ΔG(233 K)‡ = 44 ± 1 kJ mol−1). 相似文献
62.
Andrea Schfer Manfred Hesse Max Viscontini Henning Paul Berthold Fischer 《Helvetica chimica acta》1995,78(7):1763-1776
The experimental conditions developed for the detection of rather stable radical cations in solution by electrospray-ionization mass spectrometry (ESI-MS) of a FeII complex of 2-amino-5,6,7,8-tetrahydro-5-methylpteridin-4 (3H)-one ( 1c ) are used to observe the formation of the more unstable radical cations formed from 2-amino-5,6,7,8-tetrahydropteridin-4(3H)-one ( 1a ) and tris(pentane-2,4-dionato)iron(III) ([FeIII(acac)3]; 4 ) and to monitor their oxidation to the corresponding p-quinonoid dihydropterin complexes. These results contribute to the understanding of the important role played by 6β-5,6,7,8-tetrahydro-L -biopterin ( 1b ; a homologue of 1a ) together with iron as constituent of some cofactors. The complexes obtained from 1a and iron may be considered, e.g. as a model of the cofactor of the phenylalanine hydroxylase. Moreover, we describe an improved synthesis of 1c . 相似文献
63.
We have performed two molecular-dynamics simulations to study the structural and dynamical properties of water at the interface with phospholipid bilayers. In one of the simulations the bilayer contained neutral phospholipid molecules, dioleoylphosphatidylcholine (DOPC); in the second simulation the bilayer contained charged lipid molecules, dioleoylphosphatidylserine (DOPS). From the density profile of water we observe that water next to the DOPS bilayer is more perturbed as compared to water near the DOPC bilayer. Using an energetic criterion for the determination of hydrogen bonding we find that water molecules create strong hydrogen bonds with the headgroups of the phospholipid molecules. Due to the presence of these bonds and also due to the confinement of water, the translational and orientational dynamics of water at the interface are slowed down. The degree of slowing down of the dynamics depends upon the location of water molecules near a lipid headgroup. 相似文献
64.
Murat Acemoglu Peter Uebelhart Max Rey Conrad Hans Eugster 《Helvetica chimica acta》1988,71(5):931-956
Syntheses of Enantiomerically Pure Violaxanthins and Related Compounds The epoxides 16 and ent- 16 , prepared by Sharpless-Katsuki oxidation of 15 in excellent yield and very high enantiomeric purity, were used as synthons for the preparation of (+)-(S)-didehydrovomifoliol (45) , (+)-(6S, 7E, 9E)-abscisic ester 46 , (+)-(6S, 7E, 9Z)-abscsic ester 47 , (?)-(3S, 7E, 9E)-xanthoxin (49) , (?)-(3R, 7E, 9E)-xanthoxin (50) , (3S, 5R, 6S, 3′S,5′R, 6′S, all-E)-violaxanthin (1) (3R, 5R,6S,3′R,5′R,6′S, all-E)-violaxanthin (55) and their (9Z) (see 53 , 57 ), (13Z) (see 54 , 58 ), and (15Z) (see 60 ) isomers. The novel violadione ( 61 ) was prepared from 1 by oxidation with DMSO/Ac2O. By base treatment, 61 was converted into violadienedione (62) , a potential precursor of carotenoids with phenolic end groups. 相似文献
65.
Roland Prewo Jost H. Bieri Subhendu Narayan Ganguly Max Viscontini 《Helvetica chimica acta》1982,65(3):1094-1099
The Configuration at C(6) of Natural 5,6,7,8-Tetrahydro-L-biopterin and of its Pentaacetate The structure of (6.R)-pentaacetyl-5,6,7,8-tetrahydro-L-biopterin, one of two diastereoisomers obtained by catalytic hydrogenation and subsequent acetylation of L-biopterin, has been determined by X-ray diffraction analysis. The space group is P212121, a=8,053(l), b=14,955(3), c= 21,502 (4) Å. The asymmetric unit contains one molecule of the biopterin derivative and one of ethyl acetate. The R-configuration can be assigned to C(6) by reference to the known configurations of the other asymmetric C-atoms. As hydrolysis of this diastereoisomer yields the natural 5, 6,7,8-tetrahydro-L-biopterin, the latter also possesses the (6 R)-configuration. 相似文献
66.
Conformational analysis of 5,6,7,8-tetrahydropteroic acid and 5,6,7,8-tetrahydro-L -folic acid In the 360-MHz-1H-NMR.-spectrum of (6R, S)-9,9-dideuterio-5, 6, 7, 8-tetrahydropteroic acid (racemic) (XIII) (AMX-System, Fig. 4) and (6R, S)-9,9-dideuterio-5, 6, 7, 8-tetrahydro-L -folic acid (diastereomeric) (XVI) the Ha–C(6) and Ha–C(7) show a vicinal coupling constant of 6,7 Hz and the Ha–C(6) and He–C(7) one of 3,2 Hz. The first coupling constant provides evidence for an approximate trans-diaxal arrangement of Ha–C(6) and Ha–C(7), and the second for a gauche conformation of Ha–C(6) and He–C(7). The tetrahydropyrazine ring in the racemic 5, 6, 7, 8-tetrahydropteroic acid (III) and in the diastereomeric 5, 6, 7, 8-tetrahydro-L -folic acid (XVII) exists therefore in a half-chair conformation with a pseudoequatorial position of the side chain at C(6) (Fig.5). 相似文献
67.
PHOTOTROPISM IN PHYCOMYCES MUTANTS LACKING β-CAROTENE 总被引:1,自引:0,他引:1
Abstract. β-carotene and riboflavin are considered as the major candidates for the photoreceptor for physiological responses to blue light in Phycomyces and a number of other organisms. Mutants of Phycomyces blocked in all six steps of the biosynthesis of β-carotene from phytoene contain no detectable β-carotene (less than 4 times 10-5 of wild-type amount) but exhibit phototropic responses identical to wild-type. Moreover, wild-type Phycomyces , while abundant in trans -β-carotene, contains no detectable cis -β-carotene, sometimes proposed as a photoreceptor candidate on the basis of the close similarity of the cis -species absorption spectrum in the near UV region to many action spectra for blue-light responses. These results indicate that β-carotene cannot be the photoreceptor for phototropism in Phycomyces. 相似文献
68.
69.
Max Winter Karl H. Schulte-Elte Alain Velluz Josef Limacher Wilhelm Pickenhagen Günther Ohloff 《Helvetica chimica acta》1979,62(1):131-134
Aroma Constituents of the Purple Passion Fruit. Two New Edulan Derivatives The isolation of (2R*, 4S*, 4aS*, 8aS*)-4,4a-epoxy-4,4a-dihydroedulan ( 1 ), and (2R*, 3S*, 8aS*)-3-hydroxyedulan ( 2 ), two new constituents of the purple passion-fruit (Passiflora edulis SIMS ), is reported. Racemic epoxide 1 was synthesized by oxidation of edulan 6 with peracidic acid, and racemate of alcohol 2 was obtained by reduction of ketone 7 , one of the chromic acid oxidation-products of edulan 6 . 相似文献
70.
Solvolysis of 4-Alkydenbicyclo[3.2.0]hept-2-en-6-oles. Synthesis of 1-Vinylfulvenes and 8,8-Diphenylheptafulvene Four 4-alkylidenebicyclo[3.2.0]hept-2-en-6-ones 2–5 , obtained via ketene cycloaddition to fulvenes, were reduced to separated mixtures of the ‘endo’ -alcohols ‘endo’- 6 to ‘endo’- 9 (68–73%) and ‘exo’- 6 to ‘exo’- 9 (3–20%). Treatment of some of these alcohols with (CF3SO2)2O in CH2Cl2/pyridine caused a spontaneous solvolysis to yield unsaturated 7-membered rings as pyridinium triflates 10–12 or 1-vinylfulvenes 13 and 14 , a new class of reactive tetraenes: Both ‘endo’- 9 and ‘exo’- 9 , having two methyl groups at C(7), were converted into the vinylfulvene 13 (≈ 80%). The alcohols with two H-atoms at C(7) exhibited a stereochemically controlled reaction selectivity, inasmuch as ‘endo’- 6 to ‘endo’- 8 afforded only the corresponding 7-membered-ring pyridinium salts 10–12 (66–79%), while ‘exo’- 6 produced only the vinylfulvene 14 (77%). A stereoelectronic control argument explains the C(1), C(5)-bond cleavage with ‘endo’- B and ‘endo’– 6 -‘endo’- 8 , as well as the C(1), C(7)-bond cleavage with ‘exo’- B , ‘exo’- 6 , and with both ‘endo’- and ‘exo’- 9 . Thermolysis (120°) of the pyridinium triflates 10 and 11 yielded the 3-isopropenyl-cycloheptatrienes 18 and 19 , respectively (≈90%); similar conditions (145°) applied to the triflate 12 produced the doubly cyclized fluorene derivative 21 (60%). When the iodide 22 derived from the triflate 12 with Nal was heated in refluxing toluene, 8,8-diphenylheptafulvene ( 23 , 86%) was obtained. 相似文献