bluuebunny/crossref_metadata_2025 huggingface dataset:
Reactions of overcrowded polymethylbenzenedisulfonic acids in concentrated aqueous sulfuric acid; protiodesulfonation and intramolecular sulfonic anhydride formation
Authors: Koeberg‐Telder Ankie , Cerfontain Hans
Published: September 2010

The reaction of the three tetramethylbenzenedisulfonic acids and some lower homologues in concentrated aqueous sulfuric acid has been studied at 25deg;C. 3,4,5,6‐Tetramethylbenzene‐1,2‐disulfonic acid undergoes both intramolecular disulfonic anhydride formation (the rate of which strongly increases upon increasing the sulfuric acid acidity) and protiodesulfonation (the rate of which decreases slightly with increasing acidity) while the other disulfonic acids only undergo protiodesulfonation. The observed rate order for protiodesulfonation within the tetramethylbenzenedisulfonic acids [1,2‐ > 1,3>> 1,4‐(SO3H)2] differs strongly from that predicted on the basis of the additivity principle of substituent effects [1,3>>;1,4‐ > 1,2‐(SO3H)2]. The strongly enhanced reactivity of the 1,2‐disulfonic acid is ascribed to a greater relief of steric strain in the 1,2‐than in the other disulfonic acids, the sulfo group being more bulky than the methyl. Also, within the group of tri‐ and tetra‐methylbenzene‐1,3‐disulfonic acids, the rate of desulfonation increases with an increase in the degree of overcrowding around the sulfo group which is desulfonating. Mechanisms for the two types of reaction of the tetramethylbenzenedisulfonic acids are proposed, based on the variation of the rate constants with the sulfuric acid acidity. It is concluded that the substrate entity undergoing protiodesulfonation is the disulfonate dianion and further that the entity undergoing cyclization to the 1,2‐disulfonic anhydride is the monoprotonated 1,2‐disulfonic acid.
Synthesis of DNA fragments containing 5‐methyl‐deoxycytidine residues
Authors: van der Marel G. A. , Wille G. , Westerink H. , Wang A. H.‐J. , Rich A. , Mellema J. R. , Altona C. , van Boom J. H.
Published: September 2010

A properly protected 5‐methylated deoxycytidine (5mC) derivative has been synthesized and applied to assemble DNA fragments containing 5mCG, 5mCC and 5mC5mC sequences.
A study of mixed RuO2/TiO2 catalysts for the photochemical oxidation of water by persulfate ions, sensitised by ruthenium(II)tris(2,2′‐bipyridine)ions
Authors: Thewissen D. H. M. W. , Eeuwhorst‐Reinten M. , Timmer K. , Tinnemans A. H. A. , Mackor A.
Published: September 2010

Mixed RuO2/TiO2 catalysts with a varying RuO2/TiO2 ratio have been examined in the oxidation of water by persulfate ions under illumination with visible light, sensitised by Ru (bipy)32+. An optimum in the rate of oxygen evolution is found when the RuO2/TiO2 ratio amounts to about 10/90. A catalyst, which was prepared by precipitation of relatively small amounts of RuO2 on TiO2, displays a considerably higher activity in the photochemical oxidation of water than the mixed RuO2/TiO2 catalysts.
A simple approach to the synthesis of a membrane teichoic acid fragment of Staphylococcus aureus
Authors: Oltvoort J. J. , van Boeckel C. A. A. , de Koning J. H. , van Boom J. H.
Published: September 2010

The triflate procedure of Schmidt et al. enabled us to synthesize the glycolipid, 1,2‐di‐O‐stearoyl‐3‐O‐[6‐O‐(2,3,4‐tri‐O‐benzyl‐(3‐D‐glucopyranosyl)‐2,3,4‐tri‐O‐benzyl‐ß‐D‐glucopyranosyl)‐2,3,4‐tri‐O‐benzyl‐ß‐D‐glucopyranosyl]‐sn‐glycerol

The prefix sn stands for stereospecific numbering in accordance with the IUPAC recommendation, see: Eur. J. Bio‐chem. 2, 127 (1967).

. Phosphorylation of this compound with an activated and properly protected phosphatidyl derivative gave a phosphotriester derivative which, after deblocking of all protective groups, afforded a naturally occurring teichoic acid fragment.
Adsorption and Mössbauer studies of partially dehydrated FeCaA zeolites
Authors: van de Vloed G. , de Roy G. L. , Verhaert I. , Vansant E. F.
Published: September 2010

The physicochemical properties of the iron exchanged A‐type zeolites are affected by the degree of dehydration of the samples. Mössbauer and adsorption techniques were used to investigate the cation distributions in these zeolites. At lower degrees of hydration, a significant number of iron ions are located inside the sodalite cavities. A systematic study of the adsorption of probe gases, such as CH4, CO and CO2, was subsequently carried out and the results were correlated to the structural features of the dehydration.
Photocycloadditions of xanthenethione to allenic compounds
Authors: Kamphuis J. , Hupkes J. G. , Visser R. G. , Bos H. J. T.
Published: September 2010

The (2 + 2)‐ and (4 + 2)‐cycloaddition of triplet xanthenethione to phenyl‐, methoxy‐tert‐butoxy‐, (methylthio)‐, (tert‐butylthio)‐ and 1,1‐dimethyl‐allene gives rise to thietanes 3 and 4, and to thiopyran derivative 5, respectively. The mechanism of the reaction is discussed. In the case of thietane 3 (X = Ph), prototropy to the stable thiete 6 has been observed.
A model study of the role of the CONH2‐group in the redox co‐enzyme NAD(P)+‐NAD(P)H. chirality in 2,4‐dimethyl‐3‐carbamoylpyridinium cations
Authors: van Hooff H. J. G. , van Lier P. M. , Bastiaansen L. A. M. , Buck H. M.
Published: September 2010

Experimental verification of chirality in 2,4‐dimethyl‐3‐carbamoylpyridinium cations.
Conversion of 2‐alkylcyclopentanones into 2‐alkyl‐2‐cyclopentenones with hydrated ferric chloride and cupric chloride
Authors: Cardinale G. , Laan J. A. M. , Russell S. W. , Ward J. P.
Published: September 2010

Hydrated ferric chloride, FeCl3·6 H2O, in a polar, hydroxylic solvent converted 2‐alkylcyclopentanones directly into 2‐alkyl‐2‐cyclopentenones on heating in the presence of air. Yields of isolated products were about 40 %. The scope of the reaction is discussed. With cupric chloride, chloroketones were formed as intermediates, which could be dehydrochlorinated to 2‐alkyl‐2‐cyclopentenones in similar yields.
Synthesis of 1‐isocyano‐1‐tosylalkenes using lithio‐α‐(trimethylsilyl)tosylmethyl isocyanide
Authors: van Leusen Albert M. , Wildeman Jurjen
Published: September 2010

The previously unreported lithio derivative of α‐(trimethylsilyl)tosylmethyl isocyanide (4) has been used in an improved method for the synthesis of 1‐isocyano‐l‐tosylalkenes (1) by reaction with aromatic aldehydes, with α,β‐unsaturated aldehydes and with cyclobutanone (Peterson reaction). Different results are obtained with chloral.
The reaction of some polycyclic halides with lithium p,p′‐di‐tert‐butylbiphenyl
Authors: Stapersma J. , Kuipers P. , Klumpp G. W.
Published: September 2010

3‐Chloroquadricyclane (1), 2(4)‐chlorosemibullvalene (2a), a series of 2‐norbornyl halides and 4,4‐dichlorotetracyclo[3.3.0.02.8.03.6]octane (4) have been treated with lithium p,p′‐di‐tert‐butylbiphenyl. Lithiation (2, norbornyl halides), lithiation with rearrangement (4) and lithiation with rearrangement followed by reduction to the cycloheptatrienyl trianion (1 → 14) have been found to occur.
Synthesis and photoisomerisation of 2,3,17,18,22‐pentamethyl‐10,23‐dihydro‐1,19‐[21H,24H]‐bilindione, an unsymmetrical bilirubin model compound
Authors: de Groot J. A. , van der Steen R. , Fokkens R. , Lugtenburg J.
Published: September 2010

The unsymmetrical bilirubin model compound 2,3,17,18,22‐pentamethyl‐ 10,23‐dihydro‐1,19‐[21H,24H]‐bilindione 1c has been prepared in good yield. Irradiation of 1c leads to a photostationary state which contains three photoproducts in addition to the starting material. The photoproducts have been isolated and fully characterized as the three possible geometric isomers of 1c. Short irradiation of each of the photoisomers shows that a one‐photon one‐double‐bond isomerisation takes place.
Phosphotriester synthesis of DNA fragments on cellulose and polystyrene solid supports
Authors: van der Marel G. A. , Marugg J. E. , de Vroom E. , Wille G. , Tromp M. , van Boeckel C. A. A. , van Boom J. H.
Published: September 2010

The synthesis of a total of twelve DNA fragments on the solid supports cellulose or polystyrene via a phosphotriester approach is described. Dimer and trimer blocks, protected at the 5′‐end with the levulinoyl group, were used for chain extension in the presence of the activating agent (2,4,6‐triisopropylbenzenesulfonyl)‐3‐nitro‐1,2,4‐triazole or (mesitylenesulfonyl)‐3‐nitro‐1,2,4‐triazole. The yields of the coupling procedures are normally high and the final unprotected DNA fragments released from the solid support could easily be isolated by Sephadex G50 column chromatography.
The regiochemistry of organocopper‐induced substitution of 2,4‐pentadiynyl methanesulfinates
Authors: Oostveen E. A. , Elsevier C. J. , Meijer J. , Vermeer P.
Published: September 2010

The reaction of alkylcopper(I) compounds, RCu, with 2,4‐pentadiynyl methanesulfinates, R′CC‐CCCR″R′″OS(O)Me (1), shows a regiochemistry that depends on the size of R, R′, R″ and R′″. If the group R′ is methyl or trimethylsilyl, the reaction is regiospecific and leads to pure allenynes R′CCC(R)CCR″R′″ (2). Mixtures of allenynes 2 and pentatetraenes RR′CCCCCR″R′″ (3), however, may arise when 1, in which R′ is hydrogen, is used as substrate.
Quantum‐chemical simulation of the acid‐, base‐ and enzyme‐catalyzed isomerization of Δ5‐3‐keto steroids
Authors: Kooistra C. , Ae. Sluyterman L. A. , Buck H. M.
Published: September 2010

Δ5‐3‐Keto steroids are isomerized to Δ4‐3‐keto steroids by acid, base and enzyme catalysis. The latter reaction occurs by a suprafacial [1,3] H shift from the 4β to the 6β position. These reactions have been simulated using propene and 3‐butenal as substrates. The catalytic effect of a number of bases, B, on the migrating H atom has been studied. The MINDO/3 proton affinities of a group of bases, relative to the affinity of NH3, correlated very well with values calculated using ab initio methods with a large basis set and with experimental gas‐phase data. The semi‐empirical MINDO/3 method has been used to study catalysis by H2O, NH3, formamidine, imidazole, HCOO− and OH− on the suprafacial [1,3] H shift in propene. Similar trends in barrier heights were found with STO‐3G and 4‐31G calculations. A linear dependence of activation enthalpy upon the relative proton affinity of the catalysts could be demonstrated. As a more realistic model for the enzymatic isomerization of 3‐keto steroids, the 3‐butenal → 2‐butenal rearrangement has been studied. Distinct co‐operation between proton acceptors, B, and proton donors, AH, interacting with the carbonyl group, could be established. Acid catalysis was simulated using AH = H3O+ and B = H2O, base catalysis in the absence of AH with B = OH− and enzyme catalysis using AH = imid · H+ and B = HCOO−, MINDO/3 calculated activation enthalpies were 28.0, 8.9 and ‐1.0 kcal · mol−1, respectively. These exhibit the same sequence as the experimental values of 14.0, 11.4 and 5.0 kcal · mol−1, found under the respective conditions. The electron distributions demonstrated that the reactions proceed more readily when the ionogenic component is more pronounced in the transition state. Almost complete deprotonation of the substrate occurs in the base‐catalyzed and the enzyme‐catalyzed reactions, giving rise to intermediates similar in structure to the dienol anion and the neutral dienol, respectively. When catalyzed, suprafacial shifts were favoured over the antarafacial shifts.
Trimethylacetic formic anhydride. Improved preparation and use as a highly efficient and selective N‐formylating reagent
Authors: Vlietstra Edward J. , Zwikker Jan W. , Nolte Roeland J. M. , Drenth Wiendelt
Published: September 2010

The title compound was prepared from trimethylacetyl chloride and sodium formate in the presence of 18‐crown‐6. The mixed anhydride proved to be a very useful reagent for the N‐formylation of amines. Even amines which are unstable when deprotonated can be formylated.
Bacteriorhodopsins with a chemically modified chromophore. The light‐driven proton pump action of [13‐demethyl‐11,14‐epoxy]‐, [9‐demethyl]‐, [13‐demethyl]‐ and [9,13‐bisdemethyl]‐bacteriorhodopsin
Authors: Muradin‐Szweykowska M. , Broek A. D. , Lugtenburg J. , van der Bend R. L. , van Dijck P. W. M.
Published: September 2010

The binding of the isomers of 13‐demethyl‐11,14‐epoxy‐, 9‐demethyl‐, 13‐demethyl‐and 9,13‐bisdemethylretinal to bacterioopsin has been studied. The bacteriorhodopsin analogues formed were incorporated into phospholipid vesicles and their light‐driven proton pump action examined.

[9‐Demethyl]‐bacteriorhodopsin, with a similar light‐dark adaptation as the unmodified bacteriorhodopsin, shows 37% of the proton pumping ability of the native pigment.

Interestingly, all‐trans‐13‐demethylretinal does not form [13‐demethyl]‐bacteriorhodopsin, whereas both the 11‐ and 13‐cis isomer form a dark‐adapted [13‐demethyl] pigment analogue. This [13‐demethyl]‐bacteriorhodopsin analogue neither shows light adaptation nor pumps protons, which is in agreement with the finding that only light‐adapted bacteriorhodopsin can exert such a function.

The 13‐demethyl‐11,14‐epoxyretinal forms a light‐adapted bacteriorhodopsin analogue with a proton pump action. It does not show a dark‐adapted form.

In the 9,13‐bisdemethylretinal, the perturbation at position 9 is considerably larger than in the previous cases. The specificity of the protein‐chromophore interaction no longer being present, all‐trans, 9‐cis, 11‐cis and 13‐cis isomers form the corresponding bacteriorhodopsin analogues with proton pump ability.

These results indicate that the chromophore in light‐adapted bacteriorhodopsin can only occur in the 12‐s‐cis conformation. Furthermore, it would seem that isomerisation around the 13‐double bond is not as important in proton pumping as has generally been assumed.
Photoinduced electron transport in bi‐ and trichromophoric systems
Authors: Mes G. F. , van Ramesdonk H. J. , Verhoeven J. W.
Published: September 2010

The photophysical properties of a trichromophoric molecule (D2‐D1‐A) containing an electron acceptor (A) and two electron donors (D1,D2) are investigated. Photoinduced electron transport from D2 to A occurs effectively via D1,. If D1, is rendered inoperative by its selective protonation, the system switches to a mode of electron transport which involves direct transfer between the remote D2 and A chromophores.
Studies on polypeptides XXXVIII. An approach to the chemical semisynthesis of ribonuclease a analogues. Part II. Semisynthesis of alanyl‐Nϵ‐octaacetimidoyl‐S‐protein and Nϵ‐octaacetimidoyl‐ribonuclease(14–124)
Authors: Hoogerhout P. , Kerling K. E. T.
Published: September 2010

The semisynthesis of Alanyl‐Nϵ‐octaacetimidoyl‐S‐protein and Nϵ‐octaacetimidoyl‐ribonuclease(14‐124) is reported. The N‐hydroxysuccinimide esters of (tert‐butyloxycarbonyl)‐l‐alanine and of a partially protected ribonuclease heptapeptide(14‐20) were coupled with Nϵ‐octaacetimidoyl‐S‐protein. After reaction of the coupling products with trifluoroacetic acid, the N‐terminal unprotected proteins were obtained.
Photochemical reactions of some aromatic thiones with bis(tert‐butylthio)ethyne. Isolation and properties of thietes, the photochemical (2 + 2)‐cycloadducts and their isomeric α,β‐unsaturated dithioesters
Authors: Brouwer A. C. , George A. V. E. , Bos H. J. T.
Published: September 2010

Photochemical reaction of some aromatic thiones 2 with bis(tert‐butylthio)ethyne 1 affords the α,β‐unsaturated dithio esters 4 via a (2 + 2)‐cycloaddition reaction of the triplet‐excited thiones 2 with acetylene 1. In one case, a (2 + 2)‐cycloadduct, thiete 3o, was isolated. Spectroscopic investigations revealed that in solution there is an equilibrium between this thiete 3o and the isomeric α,β‐unsaturated dithio ester 4o. The generality of this equilibrium phenomenom is examined and discussed with respect to the substituents of the C=C‐C=S moiety of the α,β‐unsaturated dithio esters 4.
Chemistry of ketene acetals V. Catalyzed and non‐catalyzed (2 + 2)‐ and (4 + 2)‐cycloadditions between 1,2‐diketones and ketene acetals
Authors: Bakker C. G. , Scheeren J. W. , Nivard R. J. F.
Published: September 2010

Generally, 1,1‐dimethoxypropene [CH3CH=C(OMe)2, 1b] yields only (2 + 2)‐cycloadducts, viz. oxetanes (3) and bis‐oxetanes (4), in reactions with 1,2‐diketones; (4 + 2)‐cycloaddition products, viz. dihydrodioxins (5), are not formed because of their thermodynamic instability. In similar reactions of tetramethoxyethene [(MeO)2C=C(OMe)2, 1a], compounds 5, however, are obtained, when the (4 + 2)‐cycloaddition is accompanied by an increase in the stabilization energy of the diketone moiety. The difference between 1a and 1b can be ascribed to the low π‐bond energy of 1a.
On the total synthesis of the naloxones from 1‐benzylisoquinolines via 1‐bromo‐2‐(1‐phenyltetrazol‐5‐yloxy)dihydrocodeinone (Chemistry of Opium Alkaloids, Part XVII)
Authors: Crabbendam P. R. , Beyerman H. C. , Lie T. S. , Maat L.
Published: September 2010

The Delft total synthesis of morphinans starts from 1‐benzylisoquinolines (Scheme 2, 7) and gives both the morphinans with the natural (‐)‐morphine configuration and the corresponding enantiomers. This route has been used as a basis for an improved synthesis of (‐)‐naloxone and also provides the possibility of preparing (+ )‐naloxone, which is of interest in pharmacological research (Scheme 1, 6). We report here in particular on the conversion of 1‐(3,5‐dibenzyloxy‐4‐methoxybenzyl)‐1,2,3,4‐tetrahydro‐6‐methoxyisoquinoline (7) into dihydrocodeinone (2) via dihydrothebainone (1), the yield of which was raised from 6 to 17%. An improved procedure has been evolved for the conversion of noroxycodone (5) into naloxone (6).
Studies on polypeptides XXXIX. The role of the imidazole tele‐nitrogen atom of histidine‐12 in the catalytic action of RNase S′
Authors: Hoes C. , Kerling K. E. T. , Havinga E.
Published: September 2010

Of three analogues of des(15‐20)‐RNase S′, in which the active site histidyl‐12 residue has been replaced by the 3‐(2‐pyridyl)‐l‐alanyl, the 3‐(3‐pyridyl)‐l‐alanyl and the 3‐(4‐pyridyl)‐l‐alanyl residue, respectively, the enzymatic activity, using various substrates as well as the capability to bind the inhibitor 2′(3′)‐(4‐thio)‐UMP, has been determined. Inhibitor binding is quite strong for the RNase S′ analogues with either a 4‐Pya or a 2‐Pya residue at position 12 but is significantly weaker for the 3‐Pya analogue. Appreciable activity, using RNA, pU>p and C>p as a substrate, is observed for the 4‐Pya analogue, demonstrating the feasibility of replacing an essential active‐site constituent by a structurally different group while retaining the enzymatic activity. The fact that the isomeric 3‐Pya and 2‐Pya analogues are inactive shows the delicate requirements which must be met if enzymatic activity is to be observed. Evidently, a properly orientated nitrogen atom having appropriate acid/base properties is required at position 12 in RNase A or S′. The results provide compelling evidence that the imidazolyl tele‐nitrogen atom of His‐12 in the native enzyme plays an essential role in the catalysis. The imidazolyl pros‐nitrogen atom of this residue, besides providing the tele‐nitrogen atom with the appropriate pKa value, may also contribute by favouring optimal juxtaposition during the catalytic reaction.
Dynamics of DNA. A quantumchemical study
Authors: VanLier Johan J. C. , Koole Leo H. , Buck Henk M.
Published: September 2010

On the basis of CNDO‐2 and MNDO quantumchemical calculations we suggest that direct generation of Pv trigonal bipyramidal (TBP) intermediates, in pC and pT fragments of ds DNA with repetitive purine‐pyrimidine sequences, results in the B → Z transition via a selective pathway. The calculations reveal that 5′‐d(GpC), 5′‐d(GpT), 5′‐d(ApC) and 5′‐d(ApT) fragments are selected to initiate the B → Z transition. We therefore suggest that the cooperative B → Z transition can only proceed in helices having repetitive GC, GT, AC or AT sequences.
On the configurational stability of allenes and butatrienes in the presence of organocopper(I) species
Authors: Westmijze H. , Nap I. , Meijer J. , Kleijn H. , Vermeer P.
Published: September 2010

Two epimeric steroidal allenes, 1 and 2, have been interconverted by reaction with Me2CuMgCl and Me2CuLi. MeCu could also be used, although in this case the isomerisation was much slower. The 1,4‐disubstituted butatrienes 6 and 8 have also been isomerised by means of Me2CuMgCl and MeCu, while the trisubstituted butatriene Z‐7 has been isomerised into its geometric isomer using Et2CuMgCl. The isomerisations are thought to proceed through radical anions. In the case of the butatriene series, it is assumed that the carbometallation of the inner double bond by the copper(I) reagents also proceeds through the proposed radical anion intermediates.
Trans‐substitution and equilibration of phenols. Part IV. The influence of various catalysts on the trans‐tert‐butylation reaction of phenols; mechanistic aspects
Authors: Willemse F. R. J. , Kooyman E. C. , van Lamoen H. B. , de Vos D. , Wolters J.
Published: September 2010

The trans‐tert‐butylation reaction by 2,6‐di‐tert‐butyl‐4‐methylphenol has been studied for a number of phenols in the presence of different catalysts. Equilibria, as well as reaction kinetics, have been investigated. The mechanism involves the intermediacy of a tert‐butyl ether. This mechanism is supported both by the kinetics and the initially high ortho/para ratio as well as by the reversed substituent effect.
Aromatic sulfonation 86. Sulfonation of pyrene, 1‐methylpyrene and perylene
Authors: Cerfontain Hans , Laali Khosrow , Lambrechts Hans J. A.
Published: September 2010

The mono‐ and di‐sulfonation of pyrene (1a), 1‐methylpyrene (1b) and perylene (2), with SO3 in nitromethane at 0°C, has been studied. The monosulfonation of 1a, 1b and 2 leads to the almost exclusive formation of the 1‐, the 6‐ + 8‐ and the 3‐sulfonic acid, respectively, which is in agreement with predictions based on the calculated localization energies for the various positions of the respective arenes. The sulfonation of pyrene‐1‐sulfonic acid yields the 1,3‐disulfonic acid as the main product while that of both 1‐methylpyrene‐6‐ and ‐8‐sulfonic acid mainly yields the 6,8‐disulfonic acid. Perylene‐3‐sulfonic acid yields almost exclusively the 3,9‐ and/or the 3,10‐disulfonic acid. The positional reactivity orders of the pyrenesulfonic acids are determined by the (electronic) directing effect of the sulfonic acid substituent, while that of perylene‐3‐sulfonic acid is determined by the localization energies of the parent arene.
Synthesis of 6H‐benzo[cd]pyren‐6‐one, a polar constituent of carbon black
Authors: Tintel C. , van der Brugge M. , Lugtenburg J. , Cornelisse J.
Published: September 2010

6H‐Benzo[cd]pyren‐6‐one (6), a potentially carcinogenic constituent of carbon black, can be synthesized smoothly and in good overall yield (49%) from pyrene (1), by using the reactivity of the pyrene dianion.
The synthesis of precursors of labelled neuropeptides
Authors: van Nispen J. W. , Bijl W. A. A. J. , Hendrix A. M. M. , Greven H. M.
Published: September 2010

Modified amino acids which can serve as precursors in the synthesis of tritium‐labelled peptides were prepared and incorporated into biologically active peptides. Thus,p‐iodophenylalanine was incorporated at position 4 of H‐Met(O2)‐Glu‐His‐Phe‐D‐Lys‐Phe‐OH (Org 2766) and in des‐Tyr1‐γ‐endorphin. As a second labelling site, the precursor of L‐leucine, L‐methallylglycine, was incorporated in both des‐Tyr1‐γ‐endorphin and the shorter des‐enkephalin‐γ‐endorphin. Finally, the lysine residue in Org 2766 (D‐Lys) and des‐enkephalin‐γ‐endorphin (L‐Lys) was replaced by its analogue 2,6‐diamino‐4‐hexynoic acid. The precursor peptides were synthesized via the fragment condensation approach. With the exception of the methallylglycine‐containing des‐Tyr1‐γ‐endorphin, in which partial desulfurization of the methionine residue could not be prevented, these peptides could be converted by means of catalytic reduction into their respective parent compounds.
The use of immobilized enzymes in organic synthesis. Part 8. Oxidation of 1‐aryl‐3‐carbamoylpyridinium chlorides by rabbit liver aldehyde oxidase and bovine milk xanthine oxidase
Authors: Angelino S. A. G. F. , Buurman D. J. , van der Plas H. C. , Müller F.
Published: September 2010

Oxidation of 1‐aryl‐3‐carbamoylpyridinium chlorides with immobilized rabbit liver aldehyde oxidase gave predominantly 1‐aryl‐1,6‐dihydro‐6‐oxo‐3‐pyridinecarboxamides, together with the corresponding 1‐aryl‐1,4‐dihydro‐4‐oxo‐3‐pyridinecarboxamides.

In general, the site of oxidation by this enzyme is determined by steric factors. The rate of oxidation by free aldehyde oxidase is very sensitive to electronic effects. A more electron‐withdrawing aryl substituent increases the reaction rate for oxidation to 6‐oxo product. Consequently, a positive ρ value of about 3.6 was calculated for free aldehyde oxidase. Oxidation of these compounds by bovine milk xanthine oxidase yielded mainly 4‐oxo products. Preparative‐scale reactions with both free and immobilized xanthine oxidase gave low product yields. The oxidation rate of free xanthine oxidase is only slightly affected by substituents in the aryl group.
A new chiral base derived from nicotinamide. Preparation and chiral stability ofN,N‐dimethyl‐2,4‐dimethyl‐3‐carbamoylpyridine in various solvents
Authors: van Lier P. M. , Meulendijks G. H. W. M. , Buck H. M.
Published: September 2010

The synthesis of enantiomerically pureN,N‐dimethyl‐2,4‐dimethyl‐3‐carbamoylpyridine is given. A model is outlined for its chiral stability in dependence of the solvent.
The palladium(0)‐catalysed formation of 3‐methoxy‐1,3‐butadienes from methoxypropadiene derivatives and organozinc compounds
Authors: Kleijn H. , Westmijze H. , Meijer J. , Vermeer P.
Published: September 2010

The smooth conversion of the readily available compounds, H2C=C(OMe)‐CR2′‐X (1; X = OC(O)Me or OS(O)Me), with R‐ZnCl reagents, using Pd[PPh3]4 as catalyst, is described. It is shown that via this route several 3‐methoxy‐1,3‐dienes H2C=C(R)‐C(O)Me)=CR2′ (2), in which the group R is 1‐alkenyl, aryl, 1,2‐alkadienyl or 1‐alkynyl, can be prepared. The results obtained with R‐Cu or R2CuM were generally inferior to those found with the zinc compounds.
Carbon‐carbon bond forming reactions of ω‐oxylactams in acid and neutral medium
Authors: Speckamp W. N. , de Boer J. J. J.
Published: September 2010

1,3‐Dicarbonyl compounds and hydroxybenzenes condense under the influence of acid with ω‐hydroxylactams 1–7 in an intermolecular process, thereby affording ω‐alkylated lactams 8–13. The reactive intermediate in the carbon‐carbon bond forming step is a cyclic N‐acyliminium ion. The intramolecular variant affords keto ester 19. Upon activation of the ω‐hydroxylactam as a hexafluoroisopropoxy ester, condensations with cyanide in aprotic polar solvents under neutral conditions become possible.
t‐Butyldimethylsilyl (TBDMS) as protective group in carbohydrate chemistry migration of the tbdms group in trans‐diol systems
Authors: van Boeckel C. A. A. , van Aelst S. F. , Beetz T.
Published: September 2010

In the presence of base the t‐butyldimethylsilyl (TBDMS) protective group is able to migrate between trans‐diaxial hydroxyl functions of carbohydrates.
Etudes spectrales de la stéréoisomérie de dérivés de l'aldehyde malonique
Authors: Kirsch G. , Mieloszynski J. L. , Paquer D. , Andrieu C. G.
Published: September 2010

A number of aromatic derivatives of malonaldehyde have been studied by NMR (13C, 1H) and IR. These techniques show that these compounds exist in solution as Z enol form magnified image. For nitrile derivatives magnified image, the Z as well as the E form has been identified. A detailed study of the 13C chemical shifts of these compounds is reported.
The amination of 3‐nitro‐1,5‐naphthyridines by liquid ammonia/potassium permanganate. A new and convenient amination method
Authors: Wozniak M. , van der Plas H. C. , Tomula M. , van Veldhuizen A.
Published: September 2010

Treatment of a solution of 3‐nitro‐2‐X‐1,5‐naphthyridines (X = H, OC2H5, Cl, NH2, OH) in liquid ammonia with potassium permanganate gives the corresponding 4‐amino‐3‐nitro‐2‐X‐1,5‐naphthyridines in moderate to good yields.

From 1H NMR spectroscopy, good evidence has been obtained for the intermediacy of 4‐amino‐1,4‐dihydro‐3‐nitro‐2‐X‐1,5‐naphthyridines in these amination reactions.
Lithiation of cyclopropane rings promoted by intramolecular alkoxy groups
Authors: Klumpp G. W. , Kool M. , Veefkind A. H. , Schakel M. , Schmitz R. F.
Published: September 2010

Cyclopropane C‐H separated from an alkoxy group by one, two or three carbon atoms can be lithiated if intramolecular coordination between Li and OR is possible in the reaction product.
Synthesis of arylsulfonimidoyl fluorides and their use in the preparation of (arylsulfonimidoyl)methyl isocyanides. Partial resolution of optically active S‐phenyl‐N‐tosylsulfonimidoyl fluoride
Authors: van Leusen Daan , van Leusen Albert M.
Published: September 2010

N‐Tosyl‐ and N‐methyl‐substituted sulfonimidoyl fluorides (2) have been synthesized from the corresponding chlorides by displacement with fluoride ion. S‐Phenyl‐N‐tosylsulfonimidoyl fluoride (2a) is a stable (persistent) shelf compound, which has been used for the synthesis of (S‐phenyl‐N‐tosylsulfonimidoyl)methyl isocyanides (4). The latter compounds form a new class of derivatives of methyl isocyanides, which, much like tosylmethyl isocyanides, form azoles by baseinduced cycloadditions to unsaturated substrates. Fluoride 2a has been partially resolved into its enantiomers.
Base‐catalysed isomerization of 7‐(methoxycarbonyl)‐1,3,5‐cycloheptatriene
Authors: Zwaard A. W. , Prins M. D. , Kloosterziel H.
Published: September 2010

In basic alcohol, 7‐(methoxycarbonyl)‐1,3,5‐cycloheptatriene (7b) forms its 2‐, 3‐ and 1‐isomers (viz. 2b, 3b and 1b) in successive reactions. All isomers show specific hydrogen exchange in CD3ONa/CD3OD. For 3‐ and 1‐(methoxycarbonyl)‐1,3,5‐cycloheptatriene vinylic hydrogen atoms are exchanged rather than the “allylic” 7‐H atoms.
Bis[2‐(methylsulfonyl)ethyl] phosphochloridate, a new phosphorylating agent
Authors: Beld A. , Claesen C. A. A. , Roersma E. S. , Schippers W. J. M. , Keizer L. M. , Tesser G. I.
Published: September 2010

This communication describes the application of the 2‐(methylsulfonyl)ethyl group (Mse) as a base‐labile protecting group for the two hydroxyl functions in phosphoric acid monoesters. Due to its perfect stability towards acids, the Mse group can function as a stable protecting group in a phosphochloridate, providing a suitable phosphorylating agent. Some model phosphorylations are presented, and the reaction is applied to the synthesis of bis[2‐(methylsulfonyl)ethyl] tyrosine phosphate. Removal of the Mse functions is achieved effectively and extremely rapidly in alkaline media. The estimation of the minimum conditions necessary for the removal of one or both Mse functions from bis[2‐(methylsulfonyl)ethyl] p‐nitrophenyl phosphate and from a tyrosine derivative is described.
The reactivity of the anion of 2‐(diethylamino)‐5‐phenyl‐3H‐azepine. Synthesis of 3‐substituted 2‐(diethylamino)‐5‐phenyl‐3H‐azepines
Authors: Streef J. W. , van der Plas H. C. , van Veldhuizen A. , Goubits K.
Published: September 2010

Deprotonation of 2‐(diethylamino)‐5‐phenyl‐3H‐azepine (1) with different base systems yields an anionic species, which, on treatment with appropriate electrophiles, gives the 3‐substituted derivatives of 1.
Reactivity of octachlorocyclotetraphosphazene towards alkyllithium reagents; formation of bi(cyclotetraphosphazenes)
Authors: Winter Herman , van de Grampel Johan C.
Published: September 2010

Reactions of octachlorocyclotetraphosphazene (NPCl2)4 with methyl lithium and isopropylalcohol or alkyl iodides afford hydrido‐phosphazenes and bi(cyclotetraphosphazenes). A reaction mechanism, based on an initial metal‐halogen exchange process, is proposed.
Electrochemical behaviour of horse‐heart cytochrome‐c
Authors: Schreurs J. , Veugelers P. , Wonders A. , Barendrecht E.
Published: September 2010

A quasi‐reversible electrochemical behaviour of horse‐heart cytochrome‐c is obtained at gold and platinum electrodes in the presence of 4, 4′‐bipyridine. Transparent tin‐dioxide and glassy‐carbon electrodes, modified with pyridine groups, also give rise to a quasi‐reversible response of cytochrome‐c. From impedance measurements and from cyclic‐ and ac‐voltammetry at the gold an platinum electrodes, reaction rate constants (k0′) of 0.6·10−4 to 1.4·10−4 m·s−1 were determined for cytochrome‐c in the presence of 4, 4′‐bipyridine. In both cyclic‐ and ac‐voltammograms, an adsorption peak is observed at −0.2 V vs. SCE. This peak is ascribed to strong adsorption of both ferri‐ and ferrocytochrome‐c. The 4, 4′‐bipyridine molecule creates a suitable interface at the electrode surface. Although no interaction between 4, 4′‐bipyridine and cytochrome‐c could be detected in solution, a specific interaction is believed to be present between adsorbed 4, 4′‐bipyridine and cytochrome‐c.
Gas‐phase thermolysis oftert‐butyl hydroperoxide with benzene and chlorobenzene in the temperature range 200‐300°C
Authors: Mulder Peter , Louw Robert
Published: September 2010

Thermolysis oftert‐butyl hydroperoxide (1) in nitrogen with an excess of benzene in the temperature range 200‐300°C, leads to biphenyl (2) as the only observable benzene‐derived product. With chlorobenzene, dichlorobiphenyls (4) are formed, together with chlorobiphenyl (5),ca.12% on4, and phenol (20‐25% on4); chlorophenols are not produced. The use ofca.equimolar quantities of iodine based on1results in formation of iodobenzene (3) and chloroiodobenzenes (7), respectively, at the expense of biaryl. In air, chlorobenzene and1produce chlorophenols (8), biaryl then being a minor product.

Hydroxyl radicals produced from1abstract hydrogen from benzene to give phenyl radicals (Ph•) which, in nitrogen, arylate benzene. From isomer distributions of7and of4it is inferred that hydrogen abstraction from chlorobenzene leads to chlorophenyl radicals, with a ratioo/m/p∼ 24/52/24. With chlorobenzene,ipsosubstitution, PhCl +•OH→PhOH, also takes place. In the presence of oxygen or iodine, formation of biaryls involves irreversible addition of (chloro)phenyl radical, the intermediate adduct radicals reacting with oxygen or iodine. In nitrogen, however, the first step in arylation is reversible. Apart from undergoing O‐O bond homolysis,1is attacked by•Me (formed from Me3CO•) and, to some extent, by aryl radicals. A large arene/1intake ratio (> 100), or the addition of either iodine or air suppresses ‐ or even prevents ‐ free‐radical‐induced decomposition of1.
Tetraaza‐macrocyclic cobalt(II) and nickel(II) complexes as electron‐transfer agents in the photo(electro)chemical and electrochemical reduction of carbon dioxide
Authors: Tinnemans A. H. A. , Koster T. P. M. , Thewissen D. H. M. W. , Mackor A.
Published: September 2010

The potential of a number of tetraaza‐macrocyclic complexes of cobalt and nickel to mediate the photoreduction of carbon dioxide has been studied. Carbon monoxide and hydrogen are the main products, which result from illumination of an aqueous solution containing Ru(2, 2′‐bipyridine)2+3 as sensitizer, ascorbic acid as sacrificial eletron donor and a tetraaza‐macrocyclic complex as relay. Their ratio strongly depends upon the relay compound used. The complexes can be used as electrocatalysts for CO2 reduction at a mercury electrode since they lower the overpotential for CO2 reduction showing turnover numbers/hour of approximately 3. A minimum potential is required to induce reaction of electrocatalysts and CO2 (and H2O).

Finally, the redox properties of the macrocyclic metal complexes at p‐GaP and p‐GaAs photocathodes in acetonitrile are compared with those observed at Pt.
RMN 13C de thiocétones ‐ rǒle du groupement thiocarbonyle
Authors: Mieloszynski J. L. , Schneider M. , Paquet D. , Andrieu C. G.
Published: September 2010

The shielding effects of the sulfur atom on neighbouring carbons in 36 thioketones have been characterized by 13C NMR. The results are compared with those for the carbonyl derivatives. The importance of these data for structural elucidations is discussed.
On the bromination of 1,2,3‐triphenylazulene
Authors: de Wit Peter , Lambrechts Hans J. A. , Cerfontain Hans
Published: September 2010

The bromination of 1,2,3‐triphenylazulene (1) with a tenfold excess of bromine in CHCl3/CCl4 as solvent yields 5,7‐dibromo‐1,3‐bis(p‐bromophenyl)‐2‐phenylazulene and not a dibromo derivative as reported earlier1,2. With 1.0 equivalent of bromine or 2.0 equivalents of NBS, a mixture of the 5‐bromo and 5,7‐dibromo derivatives of 1 is obtained.
Molecular dynamics computer simulation as a tool for the analysis of solvation: A study of dilute aqueous solutions of 1,4‐dioxane and 1,3‐dioxane
Authors: Remerie Klaas , van Gunsteren Wilfred F. , Engberts Jan B. F. N.
Published: September 2010

It is shown how the computer simulation technique of molecular dynamics (MD) can be used to obtain a detailed picture of the static and dynamic properties of a solution at the atomic level. The method is applied to the solvation of a single molecule of 1,4‐dioxane and 1,3‐dioxane dissolved in 122 water molecules. The structure of the solvation shell was found to be clathrate‐like although the dioxane oxygen atoms disturb this arrangement considerably. This is especially apparent for 1,3‐dioxane as a result of its large dipole moment and the favorable position of its oxygen atoms for double hydrogen bonding. Generally, comparison of simulated properties with available experimental data shows good agreement. Consideration of both static and dynamic properties leads to the conclusion that there is a balance between structure‐breaking and structure‐making properties for 1,4‐dioxane. By contrast, 1,3‐dioxane is definitely structure‐breaking. The hydration shell of 1,3‐dioxane is clearly more labile than that of 1,4‐dioxane.
A comparative investigation of 1,4‐pentamethylene and 1,4‐hexamethylene Dewar benzene: Evidence for the intermediate formation of [5]paracyclophane
Authors: van Straten J. W. , Turkenburg L. A. M. , de Wolf W. H. , Bickelhaupt F.
Published: September 2010

The synthesis of the title compounds 1a and 1b is described. Starting from the corresponding 1,2‐dimethylenecycloalkanes 6, the compounds 1 were obtained in four steps, viz. addition of dichlorocarbene, reduction with triphenyltin hydride, treatment with potassium tert‐butoxide and silver‐ion‐catalyzed rearrangement. In the last step, the 1,2‐isomers 11 of 1 were also formed, and their thermal rearrangement to the benzocycloalkenes 4 is briefly described. Compound 1b rearranged to its aromatic isomer [6]paracyclophane (2b) both thermally (60°C in solution, 100‐460°C flow pyrolysis) and under silver‐ion catalysis at room temperature; in this latter reaction, the initially formed 2b was gradually further isomerized to 4b. At higher temperatures, 2b rearranged to the spirotrienes 3b and finally fragmented to give p‐ethylstyrene (17). From 1a, the spirotriene 3a and benzocycloheptene (4a) were obtained by thermolysis and by silver‐ion catalysis, respectively. The mechanism of these reactions is discussed and it is concluded that [5]paracyclophane (2a) is a transient intermediate in the reaction of 1a.
A convenient method for the preparation of terminal methyl phosphates of nucleic acids
Authors: Wreesmann C. T. J. , van den Hoogen Y. Th. , Ledeboer A. H. , van der Marel G. A. , van Boom J. H.
Published: September 2010

The reagent 2‐chlorophenyl bis(1‐benzotriazolyl) phosphate has been used for the preparation of 5′‐O‐(methyl phosphate) esters of the dimers TpT, UpU, Upm26A and m26ApU, as well as 3′,5′‐bis‐O‐(methyl phosphate) esters of uridine (U) and the minor ribonucleosideN6,N6‐dimethyladenosine (m26A). A convenient synthesis of a non‐terminal (9) and a terminal (10) building unit of m26A is also reported.
Degradation of polypyrrole‐modified electrodes in a chloride containing medium
Authors: Vork F. T. A. , Ubbink M. T. , Janssen L. J. J. , Barendrecht E.
Published: September 2010

The behaviour of a polypyrrole‐modified electrode in an aqueous 0.5 M HCl solution at high anodic potentials was studied. Electrochemical experiments and 13C‐NMR analysis showed a decrease in conductivity, due to the formation of CCl bonds in the pyrrole ring structure.
Studies on borate esters III. Borate esters of D‐mannitol, D‐glucitol, D‐fructose and D‐glucose in water
Authors: Makkee M. , Kieboom A. P. G. , van Bekkum H.
Published: September 2010

A combination of 11B and 13C NMR spectroscopy with several model compounds has been used to elucidate the nature of the ester formation between borate and D‐mannitol, D‐glucitol, D‐fructose and D‐glucose in aqueous solution at pH 6‐12 and at 25 °C. At high carbohydrate/borate ratios, D‐mannitol shows the selective formation of bis(D‐mannitol) 3,4:3′4′ ‐borate, whereas D‐glucitol forms a mixture of six different bis(D‐glucitol) borate esters involving both 2,3‐ and 3,4‐dihydroxyl moieties. Bis(D‐fructose) and bis(D‐glucose) borate esters consist of pairs of diastereomers of the 2,3‐β‐and 1,2‐α‐furanose moieties, respectively. At low carbohydrate/borate ratios, mono‐, di‐ and, sometimes, tri‐borate esters are formed, e.g. mixture of α‐D‐glucofuranose 1,2:3,5‐diborate and α‐D‐glucofuranose 1,2:5,6‐diborate for D‐glucose and a mixture of β‐D‐fructopyranose 1,2:4,5‐diborate and β‐D‐fructopyranose 2,3:4,5‐diborate for D‐fructose. The overall stability constant for the borate di‐esters of D‐mannitol, D‐glucitol and D‐fructose is about two orders of magnitude higher than that of D‐glucose.
C‐Nitroso compounds. Part XXXVII. The reactivity of α‐chloronitroso compounds towards organoaluminium reagents
Authors: Lub J. , Beekes M. L. , de Boer Th. J.
Published: September 2010

With sterically unhindered and certain moderately hindered α‐chloronitroso compounds 1 trimethylaluminium at low temperature gives, via complexes 2 and 3, the methyl nitrones 4 (Scheme 1). Several intermediate complexes 3 lose methane upon heating and rearrange to α‐chloroimines 5 (Scheme 2), the structure of which is determined by that of the precursors (E‐ or Z‐geometry; cf. Scheme 6).

More sterically hindered α‐chloronitroso compounds containing quaternary carbon undergo C‐C rupture when treated with trimethylaluminium, thus forming hydroxamic acid chlorides, formally HCI adducts of nitrile oxides (cf. 8j in Scheme 3; 8k in Scheme 4). In the latter case, subsequent reactions lead to overall ring enlargement, i.e. formation of the seven‐membered cyclic oxime 12. With triethyl‐aluminium and triisobutylaluminium, α‐chloronitroso compounds are mainly reduced to oximes and the isomeric amides (Scheme 7).
Scission of the epoxy ring in 4,5α‐epoxymorphinans: A convenient synthesis of β‐dihydrothebaine, 6‐demethoxy‐β‐dihydrothebaine and desoxycodeine‐A (Chemistry of opium alkaloids, Part XXI)
Authors: Linders J. T. M. , Adriaansens R. J. O. , Lie T. S. , Maat L.
Published: September 2010

The use of zinc and aqueous potassium hydroxide for the reductive epoxy ring opening of thebaine (1) and 6‐demethoxythebaine (2) is described. The reaction affords exclusively β‐dihydrothebaine (3) and 6‐demethoxy‐β‐dihydrothebaine (4), respectively. The synthesis of desoxycodeine‐A (9) has been improved and evidence for its configuration is discussed.
Polymer‐supported synthesis of deoxyoligonucleotides using in‐situ prepared deoxynucleoside 2‐cyanoethyl phosphoramidites
Authors: Nielsen J. , Taagaard M. , Dahl O. , Marugg J. E. , van Boom J. H.
Published: September 2010

The easily accessible reagent 2‐cyanoethyl‐bis (diisopropylamino) phosphoramidite is shown to be suitable for the in‐situ, 1H‐tetrazole catalysed, preparation of d‐nucleoside‐3′‐phosphoramidites. The latter compounds could be applied successfully as building blocks in a solid‐phase DNA synthesis using an automated DNA synthesizer.
Synthesis of spin‐labelled di‐ and tri‐2‐deoxyadenylates
Authors: Claesen C. A. A. , Daemen C. J. M. , Tesser G. I.
Published: September 2010

Two spin‐labelled dinucleotide derivatives and two spin‐labelled trinucleotide derivatives have been prepared and their constitution established using HPLC and enzymatical degradation. 1H NMR spectroscopy was performed prior to and after reduction of the spin label with ascorbic acid. 2‐(tert‐Butylsulphonyl)ethyl N6‐(diphenylacetyl)‐5′‐O‐(4,4′‐dimethoxytrityl)‐2′‐deoxyadenosyl phosphoromorpholidite (4) was prepared and used for the phosphitylation of N6‐(diphenylacetyl)‐3′‐O‐levulinoyl‐2′‐deoxyadenosine (7) to give the dinucleotide derivative 8 and the trinucleotide derivative 10. The spin label was introduced in the 5′‐position of these compounds, using (5), to give compounds 9 and 11 in the fully protected form.

Unexpectedly, the stability of the spin label was found to be so high that the function could be used as the definite blocking for the 3′‐hydroxyl group in the 2′‐deoxyadenosine moiety. Thus, starting from 3 and using compound 5, 2‐(tert‐butylsulphonyl)ethyl N6‐(diphenylacetyl)‐2′‐deoxy‐3′‐adenosyl 1‐oxyl‐2,2;6,6‐tetramethyl‐4‐piperidinyl phosphate (6) was obtained. This compound afforded the protected di‐ and tri‐nucleotide derivatives 12 and 13, following one or two phosphitylations with 4 and subsequent oxidation.

Deprotection of the derivatives 9,11,12 and 13 to the spin labelled end‐products was achieved in one step using concentrated aqueous ammonia.
C‐Nitroso compounds. Part XXXVIII: Radical reactions of α‐chloro‐nitroso compounds with trialkylaluminium‐ether complexes
Authors: Lub J. , Beekes M. L. , de Boer Th. J.
Published: September 2010

Ether complexes of trialkylaluminium compounds react with α‐chloro‐nitroso compounds via radicals which can abstract hydrogen from various solvents. In the presence of olefinic solvents, radical addition to the double bond also takes place.

When the trialkylaluminium compounds are not complexed by ethers, they react with α‐chloro‐nitroso compounds predominantly via heterolytic processes1,2.
A novel synthetic route to 6‐azabicyclo[3.2.1]oct‐3‐enes via silicon directed N‐Acyliminium chemistry: Synthesis of (±)‐gabaculine
Authors: Hiemstra Henk , Klaver Wim J. , Nico Speckamp W.
Published: September 2010

Alkylation of the lithium enolate, derived from 5‐ethoxy‐2‐pyrrolidone 1 (Scheme 1), using alkyl halides containing either the vinylsilane or 2‐propynylsilane moiety, provides substrates 3 for cyclization studies passing through N‐acyliminium intermediates 4 toward the 6‐azabicyclo[3.2.1]‐octanes 5 and 7. These ring‐closure experiments are unsuccessful in the case of vinylsilanes, and an explanation for this failure is presented. Ring closures of 2‐propynylsilanes lead, in high yield, to bicyclic allenes 5, which, in a few steps (ozonolysis, Shapiro reaction), are transformed into 7. This methodology constitutes the basis of a total synthesis of (±)‐gabaculine (10). The synthesis is completed from 52 by lactam hydrolysis and sulfoxide elimination.
A 15N study of the ammonia‐induced deamination of 1‐aminopurinium salts
Authors: Jongejan H. , Kos N. J. , van der Plas H. C.
Published: September 2010

Reaction of 1‐aminoadeninium mesitylenesulfonate (1) and 1,2‐diaminopurinium mesitylenesulfonate (8) with methanolic ammonia for 17 h at 100°C leads to deamination at N(l), yielding adenine and 2‐aminopurine, respectively, as well as dideamination, yielding purine. It is very likely that 6‐hydrazinopurine is formed in the dideamination of 1 and that 2‐hydrazinopurine is an intermediate in the dideamination of 8. From both hydrazinopurines, purine is formed.

Labelling studies, using 15N‐labelled methanolic ammonia, show that, in the deamination reactions, a ring‐opening reaction (ANRORC mechanism) is involved.