Intermolecular Rearrangement Research Articles

Ring‐closure reaction of N‐arylthiomethylaroylamides to 1,3‐benzothiazines

AbstractN‐Arylthiomethylaroylamides substituted with an electron‐donating group in the meta position undergo two‐directional cyclization in the presence of phosphorus oxychloride to give both positional isomers of the 4H‐1,3‐benzothiazine derivative. The structures of the products were confirmed by 1H and 13C nmr spectroscopy. Mixed ring‐closure reactions of several N‐arylthiomethylaroylamides 3, 6, 9, 13 have shown that these conversions are introduced by a proton‐catalyzed intermolecular rearrangement.

Kinetics and thermodynamics of intra- and intermolecular rearrangement in binaphtholate complexes of titanium(IV)

Kinetics and thermodynamics of intra- and intermolecular rearrangement in binaphtholate complexes of titanium(IV)

Identification of a new genetic determinant for cell aggregation associated with lactose plasmid transfer in Lactococcus lactis

Derivatives of the lactose miniplasmid pMG820 were constructed in which a staphylococcal erm gene was inserted and in which this was accompanied by subsequent deletion of the lactose genes. The resulting plasmids were thus marked with both erythromycin resistance and lactose utilization genes in pF1132 or solely erythromycin resistance in pF1133. These plasmids retained the normal conjugation properties characteristic of lactose plasmid pLP712, including the generation by intermolecular rearrangement of high-frequency-transfer Clu+ derivatives which exhibited cell aggregation. The use of such Clu+ plasmids in a variety of mating experiments between different lactococcal strains and the observation of cell aggregation when particular mating mixtures were made led to the discovery of a new component of this conjugation system named Agg. A chromosomal gene agg was postulated to be present in some but not all strains of lactococci. High-frequency conjugation and cell aggregation thus depend on the presence of both Agg and Clu, although in a mating pair these components can be in the same or in separate strains. The Agg and Clu components may be analogous to the binding substance and aggregation substance that are involved in the hemolysin plasmid transfer system of Enterococcus faecalis, although control of their expression is different.

Studies on the thermal isomerization of N-arylmethylbenzotriazoles

The thermal isomerizations of N-benzyl-, N-diarylmethyl- and N-trityl-benzotriazole, and of N-[bis-(4-methoxyphenyl)methyl]- and N-trityl-5,6-dimethylbenzotriazole under nitrogen have been investigated. In all these cases, the N-1 isomer predominates over the N-2 isomer at thermodynamic equilibrium, to an extent which depends on the steric bulk of the N-substituent. The rate of attainment of equilibrium depends on the electronic effects of the substituents, both in the benzotriazole ring and in the migrating group. These results, in conjunction with a cross-over experiment, support a mechanism involving a heterolytic N–C bond cleavage followed by an intermolecular rearrangement.

Fragmentation of butyl acetate isomers in the drift region of an ion mobility spectrometer

Peak distortion and baseline perturbations in ion mobility spectra of butyl acetate isomers were caused by fragmentation of product ions during transport through the drift region of an ion mobility spectrometer (IMS). Extensive fragmentation of MH + and M 2H + at atmospheric pressure in air occurred with thermal energy changes ( 3 kT 2 ) of only 0.013 eV and the extent of fragmentation was influenced by the butyl isomer structure. At 150°C, major fragment ions were mass identified by IMS/mass spectrometry for t- and iso-butyl acetates as m/z 57 and for sec-butyl acetate as m/z 61. No fragmentation and only declustering from dimer to monomer ions were observed with n-butyl acetate. Fragmentation in the IMS drift region is proposed to occur by an intermolecular rearrangement mechanism through the monomer ion.

ChemInform Abstract: Intermolecular Anionic Rearrangement of the Trimethylgermyl Group in Trimethylgermylacetonitrile Anions.

AbstractTreatment of trimethylgermylacetonitrile (I) with lithium diisopropylamide results in partial formation of the digermyl derivative (II).

Use of a Tn 5 derivative that creates lacZ translational fusions to obtain a transposition mutant

We constructed a derivative of Tn 5, Tn 5ORF lac, that is capable of creating lacZ translational fusions upon transposition. Lac − strains carrying this construct formed red papillae when plated on MacConkey-lactose media. Lac + cells isolated from independent papillae expressed distinct β-galactosidase fusion proteins, suggesting that the Lac + phenotype resulted from transposition. In support of this, analysis of plasmids carrying Tn 5ORF lac prepared from these cells indicated that the Lac + phenotypes arose as a result of intermolecular rearrangements. Furthermore, a derivative of Tn 5ORF lac that contains an ochre mutation in the transposase gene formed papillae only in a supB strain. Tn 5ORF lac is useful for obtaining mutants that affect Tn 5 transposition and for creating lacZ fusions. We used the papillation phenotype to isolate a spontaneous revertant of IS 50L that promotes transposition at a 3.6-fold higher rate than IS50 R. The mutation altered the amino acid sequence of both transposase and inhibitor.

Intermolecular Anionic Rearrangement of the Trimethylgerml Group in Trimethylgermylacetonitrile Anions

Abstract Intermolecular anionic rearrangement of the trimethylgermyl group in trimethylgermylacetonitrile, bis(trimethylgermyl)acetonitrile, and tris(trimethylgermyl)acetonitrile is described.

The effect of hemoglobin ligands on the kinetics of human hemoglobin A1c formation.

HbA1c is the most prevalent of the minor human hemoglobins. It is formed by the nonenzymatic addition of glucose to the alpha-amino group of the beta chain by an initial condensation reaction and a subsequent intermolecular Amadori rearrangement. We have developed a method of analysis which utilizes high performance liquid chromatography to follow the formation of HbA1c and greatly simplifies the determination of the kinetic parameters associated with this reaction. This has allowed us to study the effects of several Hb ligands, including the hydrogen ion, on the kinetics of this glycosylation reaction. Both the initial condensation reaction and the subsequent rearrangement are shown to exhibit acid catalysis, but the rate of the condensation step is limited by the extent of protonation of the alpha-amino group. The variation in kinetic parameters as a function of hydrogen ion concentration has allowed us to determine the probable reaction mechanism of HbA1c formation by comparison to previously reported model systems of Schiff base formation and Amadori rearrangement. The formation of pre-HbA1c from deoxy-Hb shows an increased forward rate when compared to oxy-Hb. The presence of physiologic concentrations of CO2 causes a proportional decrease in both k1 and k-1. 2,3-Diphosphoglycerate causes a significant increase in the keq of the formation reaction. The effects of CO and the substitution of L-glucose for D-glucose are not significant.

Domains in viroids: evidence of intermolecular RNA rearrangements and their contribution to viroid evolution.

On the basis of sequence homology a model is proposed for five structural and functional domains in viroids. These domains include (i) a conserved central region capable of forming two alternative structures that may regulate two phases of the viroid replication cycle, (ii) a region associated with pathogenicity, (iii) a domain with high sequence variability, (iv and v) two terminal domains that are interchangeable between viroids. That the evolution of viroids has involved RNA rearrangements of domains is supported by the partial duplication of coconut cadang cadang viroid, which arises de novo during each infection. Similar RNA rearrangements have been established for animal viral defective interfering RNAs, which arise by some form of discontinuous transcription. This mechanism could account for the origin of viroids and also RNA viruses, whereby modules of genetic information may have undergone repeated exchange between RNA pathogens and the RNA of their hosts.

A relay model of lipid peroxidation in biological membranes

It is believed that in lipid peroxidation in membranes an important role is played by unoxygenated hydrocarbon radicals whose movement within the hydrocarbon moiety of the membrane is through intra- and intermolecular relay rearrangements (H-shift). In membranes containing a high concentration of polyunsaturated lipids, the radical mobility may be higher than the laterial diffusion of the lipids allowed by the microviscosity of the membrane. The action mechanism of antioxidants having a side hydrocarbon tail (e.g., tocopherols) rests upon the relay radical reaction, as a multistep process. The initial step is the relay transfer of unoxygenated free radical to the side hydrocarbon chain of antioxidant. In subsequent steps the aroxyl radical is formed by the intramolecular rearrangement of radical in an antioxidant molecule. Hence, the inhibitor interrupts the propagation chain in the membrane by the scavenge of unoxygenated hydrocarbon radical.

A relay model of lipid peroxidation in biological membranes

It is believed that in lipid peroxidation in membranes an important role is played by unoxygenated hydrocarbon radicals whose movement within the hydrocarbon moiety of the membrane is through intra- and intermolecular relay rearrangements (H-shift). In membranes containing a high concentration of polyunsaturated lipids, the radical mobility may be higher than the laterial diffusion of the lipids allowed by the microviscosity of the membrane. The action mechanism of antioxidants having a side hydrocarbon tail (e.g., tocopherols) rests upon the relay radical reaction, as a multistep process. The initial step is the relay transfer of unoxygenated free radical to the side hydrocarbon chain of antioxidant. In subsequent steps the aroxyl radical is formed by the intramolecular rearrangement of radical in an antioxidant molecule. Hence, the inhibitor interrupts the propagation chain in the membrane by the scavenge of unoxygenated hydrocarbon radical.

Halogenation of fluoroalkyl-substituted ?-ketoesters

1. The bromination of fluoroalkyl-substituted β-ketoesters using bromine gives unstable α-bromo derivatives which undergo intermolecular rearrangement to yield the starting β-ketoesters and α,α-dibromo-β-ketoesters. 2. An IR spectroscopic and dipole moment study showed that the z- and q-conformers relative to the ester C=0 bond are equally probable for the fluoroalkyl-substituted β-ketoesters.

Some stereochemical aspects of actinide coordination chemistry

Some stereochemical aspects of actinide coordination chemistry

Electrophilic aromatic substitution. Part 29. The kinetics and products of the solvolyses in aqueous sulphuric acids of 2-cyano-3,4-dimethyl-4-nitrocyclohexa-2,5-dienyl acetate: the non-occurrence of an intramolecular 1,3-migration of the nitro-group in the solvolytic reactions of the diene. The kinetics and products of nitration of 2,3-and 3,4-dimethylbenzonitrile

The kinetics in 61.8–79.5% H2SO4 and the products formed in 61.8–84.3% H2SO4 for the solvolyses of the above-named diene have been determined. The reactions are interpreted as involving concurrent elimination of nitrous acid and AAL1 generation of the same ipso-intermediate as arises in the nitration of 2,3-dimethylbenzonitrile. This intermediate reacts by intermolecular rearrangement (as is proved by the isolation from the solvolyses of 2,3-dimethylbenzonitrile and the trapping of nitronium ion by reaction with 4-fluorophenol), by nucleophilic capture by water, and by 1,2-intramolecular rearrangement to 2,3-dimethyl-4-nitrobenzonitrile. The results permit the partitioning of the overall solvolytic rate coefficient and the demonstration that the derived coefficient for the reaction competing with the elimination depends on acidity as would be expected for an AAL1 reaction. The elimination of nitrous acid is also acid-catalysed and may not be a simple E1 reaction. The solvolytic reactions of the diene do not lead to a 1,3-intramolecular rearrangement of the nitro-group and the observed 1,3-rearrangement of the diene to give 2,3-dimethyl-5-nitrobenzonitrile under non-solvolytic conditions appears to be a thermal reaction of the diene molecule. By combining the solvolysis results with those for the nitration of 2,3-dimethylbenzonitrile in 70.4–82.5% H2SO4 it is shown that the major primary consequence of the nitration is ipso-attack and that it is possible to determine the positional reactivities in the nitrile.

Intermolecular Stereoselective Pummerer Reactions of 4-(p-Chlorophenyl)thiane 1-Oxides and trans-1-Thiadecalin 1-Oxides and 2-Thiadecalin 2-Oxides with Acetic Anhydride

Abstract The Pummerer reactions of conformationally fixed 4-(p-chlorophenyl)thiane 1-oxides and trans-1-thiadecalin 1-oxides and trans-2-thiadecalin 2-oxides with acetic anhydride are either stereoselective or stereospecific, both in the absence and in the presence of a scavenger of acetic acid formed, such as dicyclohexylcarbodiimide (DCC) or 2,6-lutidine. However, the 18O-tracer experiments with the 18O-labeled sulfoxide revealed the reaction to be an intermolecular rearrangement, while the kinetic experiment with α-deuterated 4-(p-chlorophenyl)thiane 1-oxides gave sizable values of kinetic isotope effect, i.e., 2.8 for the cis isomer and 3.4 for the trans isomer. In the reaction of 4-arylthiane 1-oxides with acetic anhydride, the thermodynamically controlled product is axial 2-acetoxy-4-(p-chlorophenyl)thiane while the kinetically controlled product is the equatorial isomer which is formed in the presence of the acid scavenger, DCC. In the Pummerer reaction of the thiadecalins S-oxides the equatorial α-acetoxy sulfides are the preferential products, however, the isomer preference is more pronounced in the reaction with DCC. These observations, along with other pertinent data seem to suggest that the rate-determining step in the Pummerer reaction of these simple heterocyclic sulfoxides is E2 elimination of acetic acid from the acetoxysulfonium intermediates.

‘O-phosphobiotine analogues.’ Isolation, X-ray strurcture, and reactivity of the intermediate of the addition of hindered phosphuric esters and thioesters on the carbodi-imide group. O→N phosphoryl migration versus P–O–P bond formation

Addition reactions to carbodi-imides using oxy- and thio-phosphoric diesters crowded around phosphorus have been carried out in order to obtain a better understanding of this reaction, and to trap the intermediate, an O-phosphobiotin analogue. Oxy-compounds give a mixture of pyrophosphate and rearranged N-Phosphorylated urea or react poorly if steric hindrance at phosphorus is important. The same type of addition with thiophosphoric esters has made possible the first isolation of the intermediate of this general reaction which is relevant to pyro-phosphate and to nucleotide synthesis. This difference is rationalized in terms of the C–X–P bond lengths (X = O or S) in the intermediate, as shown by an X-ray crystallorgraphic determination of the structure of the thio-compound. With oxy-compounds, the reaction is very sensitive to steric effects, because of the short C–O–P distances involved. Formation of the intermediate is only likely if the oxyphosphorus nucleophile does not contain bulky groups, and this leads quickly to the pyrophosphate. With thio-compounds, the analogus intermediate is formed even when bulky thiophosphorus groups are present, because of the longer C–S–P distances, and is protected against intermolecular rearrangement both by the poor overlap between the nitrogen and phosphorus orbitals and by protonation if a suitable ratio of ester to dicylohexylcarbodi-imide (DCCD) is used. Moreover this intermediate is not easily attacked by the bulky (RO)2P(S)S– nucleophile and therefore accumulates. With a less favourable ratio of ester to DCCD, the reaction gives only the rearranged N-phosphorylated product. Crystals of the isolated intermediate are monoclinic, space group P21/a with four molecules in a cell of dimensions a= 15.802(3), b= 13.409(2), c= 15.050(5)Å, β= 96.82(1)°. The structure was solved by direct methods and refined by full-matrix least-squares calculations to an R value of 0.055 for 3 144 observed reflections. Several features of this molecular structure are discussed. Finally, a kinetic study of the rearrangement from C–S–P to N–P compounds shows that this reaction proceeds without the formation of any kinetically significant intermediate.

Stereoisomers of selenilimines: isolation and reactions of 9-phenylselenoxanthene-N-arylsulfonylselenilimines

The isolates cis- and trans-9phenylselenoxanthene-N-arylsulfonylselenilimines were not interconverted thermally. cis-Isomers were converted to trans-isomers by chloramine-T or -B in a fashion of S N2 type substitution. cis-Isomers did not rearrange but trans-isomers rearranged thermally to 9-arylsulfonamido-9-phenylselenoxanthenes, whereas both isomers underwent the base-catalyzed intermolecular rearrangement.

ChemInform Abstract: REARRANGEMENT OF 1‐SUBSTITUTED 3‐(3‐PYRIDYLMETHYL)NITROSOUREAS TO THEIR N‐NITROSO ISOMERS IN THE PRESENCE OF ACIDS

AbstractDie Pyridylmethylharnstoffe (I) werden zu den Isomeren (II) und (III) nitrosiert.

Rearrangement of 1-substituted 3-(3-pyridylmethyl)nitrosoureas to their N-nitroso isomers in the presence of acids.

1-(2-Chloroethyl)-(IIa), 1-isopropyl-(IIb), 1-isobutyl- (IIc) and 1-cyclohexyl-1-nitroso-3-(3-pyridylmethyl) urea (IId) isomerized to the corresponding 3-nitroso isomers (IIIa-d) in formic acid. This type of rearrangement was also observed in acetic acid, 10% hydrochloric acid, 10% sulfuric acid, methanol saturated with hydrogen chloride, and thionyl chloride. However, 1-isopropyl- (IIIb) and 1-cyclohexyl-3-nitroso-3-(3-pyridylmethyl) urea (IIId), in which the N1 substituents are bulky, hardly isomerized to the 1-nitrosoureas (IIb, d). Transnitrosation of 1-(2-chloroethyl)-1-nitroso-3-(3-pyridylmethyl) urea (IIa) with 1-methyl-3-(2-pyridylmethyl) urea gave the denitrosated compound (Ia) and a newly nitrosated compound, 1-methyl-1-nitroso-3-(2-pyridylmethyl) urea (V). It is suggested that this type of rearrangement is an acid-catalyzed, intermolecular rearrangement governed by the steric effect of the N1 substituents.