The mechanism of biomolecular methyl transfer in a methyl aminoalkanesulfonate. application of 18o isotope shifts in 13cmr spectra of sulfonic esters.

¹³Cmr spectra show complete absence of scrambling of an ¹⁸O label in $\text{1}$$\text{a}$ recovered after partial conversion to $\text{2}$$\text{a}$ thereby precluding an $\text{0}$-methylation mechanism for the bimolecular formation of $\text{2}$$\text{a}$ from $\text{1}$$\text{a}$.     

Perhalogenmethylmercapto-heterocyclen, (VII) [1] konkurrenzreaktionen elektronenarmer,substituierter aromaten um die halogenmethylmercapto- BZW. Chlorgruppe von Cl3-nFnCSCl in starken saeuren

Electron-deficient aromatics, such as 2,5-bis(trifluoromethylmercapto)thiophene ($\text{1a}$) or (trifluoromethylmercapto)benzene ($\text{8a}$), react with F₃CSCl in the presence of F₃CSO₃ as a catalyst to give mainly 3-chloro-2,5-bis(trifluoromethylmercapto)thiophen ($\text{3a}$) and 1-chloro-4- or 2-(trifluoromethylmercapto)benzene ($\text{10}$, respectively. This reaction competes with the one expected to result in 2,3,5-tris(trifluoromethylmercapto)thiophene ($\text{2a}$) and 1,4- and 1,2-bis(trifluoromethylmercapto)benzene ($\text{9}$,$\text{9′}$), respectively. Further reactions of deactivated aromatics with Cl_3-nF_nCSCl show that the chlorine substitution is in general catalysed by strong acids. Reaction mechanisms are proposed for both Substitutions. The Cl_3-nF_nCS group in aromatics exerts a -M-effect in the case of an attack of a positive ion, e.g. H^⊕, the well-known +M-effect in the case of reactions with positively polarized molecules, e.g. CF₃S^β+Cl^β-.     

Activation and transfer of oxygen XV evidence for the transient opening of the pyrazine ring in n1- and n5- alkylflavin models. 4a- to 1010- adduct isomerization and pyrazine- and pyrimidine- ring contractions.

The pyrazine ring opening is proven by rearrangements leading to benzimidazoles $\text{4}$, $\text{13}$ and $\text{14}$. A 4^a- to 10^a-adduct isomerization ($\text{6}$ → $\text{7}$) and the intermediacy of a carbonyl oxide $\text{15}$ are indicated by pyrimidine ring contractions into $\text{8}$ and $\text{9}$, respectively.     

Marine natural products: fistularin-1, -2 and -3 from the sponge Aplysina fistularis forma fulva

Three new high molecular weight bromotyrosine-related metabolites, $\text{3a}$, $\text{4a}$ and $\text{5a}$, were isolated from the sponge Aplysina ( Verongia) fistularis forma fulva, and their structures were determined from high resolution ¹H NMR and other spectroscopic data. The new metabolites are formally derived by combination of major segments of two known Aplysina metabolites $\text{1a}$ and $\text{2}$.     

Synthesis of 4a-, 4e-phenyladamantanones and 2,4-o-benzenoadamantane by π-route

The acid catalysed reaction of 4-oxa-homoadamantan-5-one ($\text{1}$) with benzene yielded a mixture of 4^a-phenyladamantan-2-one ($\text{7}$), the equatorial isomer' ($\text{8}$) and 2-phenyl-2,4-o- benzenoadamantane ($\text{9}$) A plausible reaction pathway for the occurrence of $\text{9}$. is put forward. The structure of $\text{9}$, was deduced from spectroscopic data and reaction of the proposed intermediate 2,4^a-diphenyladamantan-2-ol ($\text{11}$) with acid. 2,4-o-Ben-zenoadamantane ($\text{16}$) is prepared likewise.     

Solid solution formation in chalcopyrite systems of the type AgInX2AgMIIIX2 where M = Al,Ga, and X = S,Se

Previous (1) work on ternary chalcopyrite solid solution formation has shown that the difference in end point axial ratios ($\text{Δc}\text{a}$) is an important factor in determining the extent of mutual solubility. It was concluded that when $\text{Δc}\text{a}\text{> 0.13}$ complete solid solubility will not occur. In this work it is shown that complete solid solution formation in the systems AgAlS₂AgInS₂ ($\text{Δc}\text{a}\text{= 0.111}$), AgGaS₂AgInS₂ ($\text{Δc}\text{a}\text{= 0.11}$) and AgAlSe₂AgInSe₂ ($\text{Δc}\text{a}\text{= 0.112}$) does occur. This shows that the value of $\text{Δc}\text{a}\text{= 0.13}$ as an upper limit for solid solution formation can be approached closely.     

New polyacetylenes from the sponge Siphonochalina sp.

Six new compounds, characterized by a long unsaturated alkyl chain (nC₂₂), were isolated from a marine sponge. All compounds except for one, possess an enyne terminus on one side of the molecule and either a terminal acetylene (in four) or a propargyl alcohol on the other end. Four of the compounds were unequivocally identified mainly by spectroscopic methods.Acetylenic compounds are well-known constituents of plants: only few, however, are known from marine organisms and to our knowledge only one group of compounds contains more than a single triple bond. Among the acetylene containing marine natural products are: A group of halogenated ethers, characterized by a straight-chain C-15 carbon skeleton and a terminal enyne function which has been isolated from algae¹ and a sea hare², carotenoids³, two steroids⁴, a sesquiterpene⁵ and polyketids^6,7.A diacetylene was found in a group of several n C-22 straight-chain compounds isolated from a marine sponge⁸. One of the compounds found in the latter sponge contains, again, the enyne terminus - an end group which turns out to be quite abundant in the above and the herewith discussed compounds.In our continuing search for bioactive compounds from marine organisms we have isolated from the sponge $\text{Siphonochalina sp}$.⁹ collected at several places in the southern part of the Gulf of Eilat (the Red Sea) six n C-22 straight-chain acetylenic compounds.Extraction of the freeze-dryed sponge (petrol ether, 4% dry weight) and subsequent repeated chromatographies (LH-20 and Silica gel)^10,11 gave six closely related new compounds, named in order of polarity, Δ¹⁵-docos-1-yne ($\text{1}$; RF^12a=0.65; 0.2% based on the dry weight of the animal), octahydrosiphonochalyne ($\text{2}$; Rf^12a=0.55; 0.4%), dihydrosiphonochalyne ($\text{4}$; Rf^12a=0.44; 0.1%) siphonochalyne ($\text{3}$; Rf^12b=0.34; 0.2%), dehydrosiphonochalynol ($\text{6}$; Rf^12b=0.55; 0.1%) and siphonochalynol ($\text{5}$; Rf^12b=0.43; 0.3%).     

Action of tert-butyl azidoformate on the conjugate bases of 1,2,3,4-tetrahydro-9H-carbazole and other indole derivatives

tert-Butyl azidoformate ($\text{2}$) reacts with the conjugate bases of $\text{3a}$, $\text{7a}$, $\text{9}$ (R¹ = R² = CH₃), and $\text{9}$ (R¹ = CH₃, R² = H) to give products [$\text{4}$, $\text{8}$, $\text{12}$, and $\text{14}$, respectively] in addition to the expected N-(tert-butoxycarbonyl)indole derivatives.     

The facile (<−50°C) formation of cis-bicyclo[6.1.0]nona-2,4,6-trienes from cyclonona-1,3,5,7-tetraenes: A symmetry - forbidden reaction

The formation of the $\text{cis}$-bicyclo [6.1.0] nona-2,4,6-trienes $\text{4a}$-$\text{c}$ is not due to the sequence $\text{1}$ → $\text{2}$ → $\text{4}$, which would involve the symmetry-forbidden reaction $\text{2}$ → $\text{4}$ even at ?50°C. Rather, reaction of RX at C^4–7 of $\text{5}$, which is formed together with $\text{1}$, leads (probably via $\text{6a}$-$\text{c}$ and $\text{7a}$-$\text{c}$ to $\text{4a}$-$\text{c}$.     

Organothiometallate - alkyne addition products. The crystal and molecular structure of [(η5-C5H5)W{C(CO2Me)C(CO2Me)C(O)SMe} (CO)2]

The title compound is the final product of the reaction between dimethylacetylene dicarboxylate and [(η⁵-C₅H₅)W(SMe) (CO)₃ ]. Its molecular structure has been established by an $\text{x}$-ray analysis based on 3301 diffractometric intensities. The crystals are monoclinic, space group $\text{P}$2₁/$\text{a}$, with four molecules in a cell of dimensions $\text{a}$ = 10.323(2), $\text{b}$ = 16.016(2), $\text{c}$ = 10.437(2)», β = 103.56(2)°. After least-squares refinement $\text{R}$ = 0.036. The tungsten co-ordination is square-pyramidal, the apical site being occupied by the centroid of the cyclopentadienyl ring. The basal co-ordination sites contain two carbonyl groups and also the sulphur and σ-bonded carbon atoms of a chelating carbothiolic methyl ester ligand derived from the incoming alkyne and CO and SMe groups of the original complex. The W-S and σ-W-C bond lengths are 2.440(2) and 2.194(7)».     

atActivation and transfer of oxygen XIV. The successive accumulation of a 10a-hydroxy pseudobase and an ESR-silent blue isomer in the n1-alkylflavin model series.

Kinetic studies have substanciated the idea that the 10^a-hydroxy pseudobase $\text{2}$ is in equilibrium with a blue transient for which structure $\text{3}$ has been proposed. The rate-constants and the molar absorbances of the intermediates were estimated.     

Nucleosides, 45.-Assignment of glycosylation sites in o-hexopyranosyl-ribonucleosides by 13C-NMR

Evidence is presented that glycosylation of a ribose-OH group in nucleosides results in a significant downfield shift for the appended ¹³C nucleus and smaller upfield displacements for the adjacent carbons, providing an efficient tool for differentiating between 2′-$\text{o}$-, 3′-$\text{o}$- and 5′-$\text{o}$-glycosyl-ribonucleosides. Therewith, the products formed on enzymatic galactosylation of uridine, inosine, and adenosine are unequivocally assigned β(1→3)-glycosidic linkages ($\text{3a}$ – $\text{3c}$).     

On the mode of incorporation of leucine samples labelled at positions 5 and 2 with 3H and 14C into the isoprenylated tryptophan derivative echinuline from aspergillusamstelodami

Feeding experiments with (4$\text{S}$) [5-³H;5-¹⁴C]$\text{L}$-leucine ($\text{1a}$) and with the (4$\text{S}$) [5-³H;2-¹⁴C]-isomer ($\text{1b}$) show that incorporation into the isoprenylated tryptophan derivative echinuline ($\text{3}$), produced by $\text{Aspergillus}$$\text{amstelodami}$, involves, to a large extent, loss of the fragment enbodying the carbon atom at position 2 of the fed amino acid.     

Mecanismes d'isomerisation de l'ion C6H5COC3H7+• en phase gazeuse

Isomerisation reactions of 1-phenyl 1-butanone X^+? ($\text{1}$) and five other C₁₀H₁₂O^+? ions are demonstrated to proceed via a single intennediate ($\text{a}$); the H₂O elimination occurs from the tetralol structure ($\text{3}$).     

Bis(tricarbonyliron) complexes of P-quinodimethanes: fragmentation and isomerisation under electron impact

EI mass spectra of $\text{trans}$-η⁴,η⁴-[3,6-bis(methylene)-1,4-cyclohexadiene]-bis=(tricarbonyliron) complexes $\text{1a}$, $\text{b}$ are reported. The fragmentation pathway is rationalized by assuming a rearrangement of the $\text{trans}$-bis(tricarbonyliron) complexes into the $\text{cis}$-isomers under electron impact.     

Structure des ions [C4H7O]+ obtenus par fragmentations du [1-methylcyclobutanol]

The mass spectra of metastable molecular and fragment ions demonstrate that the loss of CH₃^. from [1-methylcyclobutanol]^.+ leads competitively to three different ions: $\text{a}$ = protonated cyclobutanone; $\text{b}$ = [n-C₃H₇CO]⁺ and $\text{c}$ = protonated methylvinylketone.     

Molecular predissociation dynamics revealed through multiphoton ionisation spectroscopy. I. The C1B1 states of H2O and D2O

The $\text{C}$¹B₁ states of H₂O and D₂O have been observed by means of three photon absorption (four photon ionisation) spectroscopy. Differences between the experimentally observed 3 + 1 multiphoton ionisation spectrum and that predicted by the appropriate asymmetric-top three-photon line-strength theory are attributed to $\text{C}$ state predissociation. Two separate predissociation mechanisms have been identified, one (heterogeneous) relying on a-axis parent molecular rotation to couple the bound B₁ state to an unbound state of A₁ electronic symmetry, the other (homogeneous) involving a second, dissociative excited electronic state of B₁ symmetry. Having established the detailed $\text{C}$ state predissociation dynamics, two photon absorption spectra of H₂O and D₂O ($\text{C}$ ← $\text{X}$) can be predicted accurately: studies of individual quantum-state-selected photofragmentation processes from H₂O($\text{C}$) are proposed.     

Synthesis of 12-layer modification of hexagonal BaFeO3 under high oxygen pressure

The modification of hexagonal BaFeO_2.85 with a = 5.700 Å and C = 28.03 Å has been synthesized at high oxygen pressure. The $\text{c}\text{a}$ ratio of 4.917 indicates that it has 12-layer sequence according to the general equation $\text{c}\text{a}\text{= 0.4107}\text{n}$. From Mossbauer spectra at 300 K, it is revealed that there are two different valance states of iron, the isomer shifts are 0.03 mm/sec for Fe⁴⁺ and 0.37 mm/sec for Fe⁴⁺, respectively.     

Synthesis,structure, and reactions of thiocarbonic acid derivatives new pentathiodipercarbonates, (RSS)2 CS, α,α,α-tris(disulfides), and the first α,α,α-tris(trisulfide)

Novel bis(perhaloalkyl) pentathiodipercarbonates $\text{5b-d}$ have been synthesized by reaction of sulfenyl chlorides with metal trithiocarbonates, and the heptathio analog $\text{21a}$ was prepared similarly. Lenthionine $\text{19}$ is the main product when diiodomethane is treated with sodium tetrathiopercarbonate. A rearrangement of bis(alkyldithio)chloromethanesulfenyl chlorides $\text{22}$ to alkyldithio) (alkyltrithio)dichloromethanes $\text{24}$ has been observed. Additions of sulfenyl chlorides and of thiosulfenyl chlorides to the thiocarbonyl compounds $\text{5}$ and $\text{21a}$ were achieved in acetonitrile. The structures of the first crystalline pentathiodipercarbonate $\text{5a}$ and α,α,α-tris(disulfide) $\text{29a}$, and of the first reported α,α,α-tris(trisulfide)$\text{31a}$ have been determined by X-ray crystallography.     

C-Metallated reformatsky intermediates. Structure and reactivity.

¹³C-NMR analysis of the Reformatsky intermediates from t-b$\text{u}$tyl-α-bromo acetate, t-b$\text{u}$tyl-α-bromo isobutyrate and t-b$\text{u}$tyl-α-bromo pr$\text{o}$pionate have evidenced C-metallated species. Their ability to act as n$\text{u}$cleophilic reagents under mild conditions and their selectivity towards h$\text{a}$logen-and oxygen containing electrophiles is reported.