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This work describes the assembly of a novel enzyme-controlled nanomachine operated through an AND Boolean logic gate for on-command delivery. The nanodevice was constructed on Au-mesoporous silica Janus nanoparticles capped with a thiol-sensitive gate-like molecular ensemble on the mesoporous face and functionalized with glutathione reductase on the gold face. This autonomous nanomachine employed NADPH and glutathione disulfide as input chemical signals, leading to the enzymatic production of reduced glutathione that causes the disruption of the gating mechanism on the mesoporous face and the consequent payload release as an output signal. The nanodevice was successfully used for the autonomous release of doxorubicin in HeLa cancer cells and RAW 264.7 macrophage cells.

We report herein the assembly of an integrated nanodevice with bi-enzymatic cascade control for on-command cargo release. This nanocarrier is based on Au-mesoporous silica Janus nanoparticles capped at the mesoporous face with benzimidazole/beta-cyclodextrin-glucose oxidase pH-sensitive gate-like ensembles and functionalized with invertase on the gold face. The rationale for this delivery mechanism is based on the invertase-mediated hydrolysis of sucrose yielding glucose, which is further transformed into gluconic acid by glucose oxidase causing the disruption of the pH-sensitive supramolecular gates at the Janus nanoparticles. This enzyme-powered device was successfully employed in the autonomous and on-demand delivery of doxorubicin in HeLa cancer cells.

We report herein a novel sensing strategy for electrochemical biosensors, by using mesoporous silica nanoparticles loaded with the redox probe methylene blue and capped with an avidin/imminobiotin stimulus-responsive gate-like ensemble as signal amplification element. As a proof of concept, an aptasensor for carcinoembryonic antigen (CEA) was constructed by attaching a biotin and thiol-functionalized anti-CEA DNA hairpin aptamer on gold nanoparticles modified carbon screen-printed electrodes. The biosensing approach relied on the unfolding of the aptamer molecule after specific recognition of CEA, unmasking the biotin residue and allowing further association with the avidin-capped mesoporous nanocarrier. Incubation with H2SO4 trigger the release of the encapsulated redox probe allowing the detection of the cancer biomarker from 1.0 pg/mL to 160 ng/mL. Keywords: Aptamer, Biosensor, Carcinoembryonic antigen, Mesoporous silica nanoparticles, Signal amplification

Au nanoparticles modified with 4-mercaptopyridine and 6-mercapto-1-hexanol were used as coordination agents to prepare a novel hybrid nanomaterial with Ag:4,4'-bipyridine nanobelts. This nanohybrid was employed to modify glassy carbon electrodes and to construct a horseradish peroxidase-based mediatorless amperometric biosensor for H2O2. The electrode, poised at -100mV, exhibited a rapid response within 4s and a linear calibration range from 90pM to 6.5nM H2O2. The biosensor showed a high sensitivity of 283A/Mcm(2) and a very low detection limit of 45pM at a signal-to-noise ratio of 3. The enzyme biosensor showed high stability when stored at 4°C under dry conditions, retaining over 96% and 78% of its initial activity after 15 and 30days of storage at 4°C, respectively.

We report herein the construction of an integrated and sensitive enzyme-powered colorimetric nanosensor for the quantification of living Saccharomyces cerevisiae. The nanodevice is provided with a pH-sensitive supramolecular nanovalve in capped benzimidazole-functionalized mesoporous silica nanoparticles with β-cyclodextrin-coated gold nanoparticles containing adatamantane-modified glucose oxidase as bioactive element. The sensing approach relies on the ability of living S. cerevisiae cells to produce invertase, which hydrolyzes sucrose to fructose and glucose. Enzymatic transformation of glucose to gluconic acid on the nanosensor surface results in the opening of the pores and delivery of an encapsulated dye, as a consequence of the local decrease in the pH. The nanosensor allows the detection of the living yeast in the range of 8·102 – 4·108 CFU/mL, exhibiting high selectivity and reproducibility, and retaining full sensing capacity after 2 weeks of storage. The nanodevice has also been successfully validated in wine samples spiked with S. cerevisiae.

A novel hybrid nanomaterial was synthesised by covalent attachment of O-carboxymethylcellulose to reduced graphene oxide. Graphene oxide was first anchored with (3-aminopropyl)triethoxysilane moieties to provide reactive primary amino groups at the basal plane. Periodate-oxidised O-carboxymethylcellulose was further covalently attached to this aminated nanomaterial through reductive alkylation with NaBH4. Stable aqueous dispersions were obtained with the resulting hybrid nanomaterial, which was used to coat glassy carbon electrodes. Furthermore, the enzyme tyrosinase was covalently immobilised and the nanostructured enzyme electrode was successfully employed for the amperometric detection of catechol in the 20 nM–56 μM range. The biosensor showed excellent analytical performance with a high sensitivity of 270 mA M−1 and a low detection limit of 0.2 nM.

Camphor- and fenchone-based bridgehead-substituted norbornan-2-ones constitute an interesting class of chiral synthons with applications in stereoselective synthesis, due to the wide variety of stereocontrolled transformations which they can undergo. Despite their synthetic value, few mass spectral studies have been realized for these compounds due to the lack of general procedures for their preparation. In this paper we have carried out an electron ionization (EI) mass spectral study of a series of heteroatomically bridgehead-substituted 7,7-dimethylnorbornan-2-ones. Their cleavage mechanisms have been rationalized on the basis of the substituent shifts, as well as on the identification of relevant peaks through accurate mass measurements and collision-induced dissociation (CID) tandem mass-spectrometric experiments. The driving force for the main fragmentation pathways of C(1)- O - and C(1)- N -substituted 7,7-dimethylnorbornan-2-ones is the α-cleavage of the C(1) C(2) bond directed by the bridgehead substituent. Further rearrangements and fragmentations of the distonic ions initially formed lead to the major ions in the spectra of all the compounds. A comparison with the known behaviour of their isomeric 3,3-dimethylnorbornan-2-ones reveals that the key bridgehead heteroatom effect controlling the fragmentation pathways can be modulated by the position of the gem -dimethyl group. As a consequence, the corresponding fragmentation patterns of both isomeric series are very different. In contrast, the fragmentation patterns of 7,7-dimethyl-2-oxo-1-norbornanesulphonamides, whose main fragmentation pathway involves homolytic S N bond cleavage, are almost identical to those displayed by their 3,3-dimethylated isomers.

Gold nanoparticles-decorated silver-bipyridine coordination polymers with intrinsic peroxidase-like activity are reported. Both morphology and mimetic enzyme activity can be tuned by rational manipulation of the nanohybrid composition. The nanomaterial was used for the electrochemical determination of H2O2 and glucose.

A novel strategy was employed to prepare a water-soluble graphene derivative by using dextran-based polymer brushes as solubilizing agents. Graphene oxide was grafted with (3-mercaptopropyl) trimethoxysilane and further decorated with Au nanoparticles. This hybrid nanomaterial was then reduced and anchored with polysaccharide-based polymer brushes by chemisorption of an end-group thiolated dextran derivative on the Au nanoparticles. The resulting hybrid nonmaterial allowed highly stable aqueous dispersions to be obtained, which were used to coat glassy carbon electrodes for the preparation of a model tyrosinase electrochemical biosensor for catechol. The enzyme electrode showed excellent electroanalytical performance with fast response in about 5 s, a linear range of 100 pM–120 nM, a very high sensitivity of 45.9 A M−1 and a very low detection limit of 40 pM for catechol.

The synthesis of chiral, rigid analogues of glycerol and cyclitols has been achieved by means of the stereocontrolled reduction of chiral bridgehead-substituted camphorquinones. This simple and easy procedure exclusively affords dihydroxy derivatives with a 2,3-cis-exo-configuration. The employment of different hydrides has also allowed the synthesis of enantiopure 2,3-dihydroxy carboxylic acids with high diastereoselectivity.

The synthesis and evaluation of a molecularly imprinted polymer (MIP) as a selective solid-phase extraction sorbent, coupled to voltammetric detection, for the efficient preconcentration and determination of sulfamethazine in milk is reported. The polymer was prepared using sulfamethazine as the template molecule, methacrylic acid as the functional monomer and ethylene glycol dimethacrylate as the cross-linking monomer in the presence of acetonitrile as the solvent. The detection of sulfamethazine was carried out by square wave voltammetry (SVW) at a glassy carbon electrode in a MeOH:acetic acid (9:1) medium. This solvent mixture was also used for the elution of the analyte from the MIP microcolumns. Optimisation of the variables involved in the sulfamethazine binding/extraction process was carried out (solvent used for rebinding, pH of the rebinding solution, eluent volume, analyte and eluent flow rates). Using solid-phase extraction cartridges, containing 0.16–0.18 g of MIP, an eluent volume of 2 ml and a sample volume of 90 ml, resulted in a nominal enrichment factor of 45, which was sufficient to analyse sulfamethazine at the maximum level permitted by the Codex Alimentarius Commission in milk (25 mg 1 −1 ). The selectivity of the MIP was evaluated by considering different substances with molecular structures similar to sulfamethazine. Sulfamethazine was determined in milk samples spiked at two concentration levels: 696 mg 1 −1 in the buttermilk obtained after milk deproteinisation, and 25 mg 1 −1 both in the buttermilk and in the milk before deproteinisation. Recoveries of practically 100% were achieved in all cases.

The electron ionization (EI) mass spectra of some new bridgehead 7,7-dimethylnorbornane-based β-amino alcohols have been studied and their fragmentation patterns compared with those of isomeric 3,3-dimethyl derivatives described by us previously. The dimethyl substitution at C7 results in a significant complication of the spectra, although all compounds show a C1–C2 bond cleavage with charge location at the nitrogen atom that leads to the base peak. Thus, two main fragmentation patterns dominated by cyclopentenylimmonium or methyleneimmonium ions are described depending on the position of the amino group in the norbornane framework (C1 or C2, respectively), as well as other secondary routes that can explain the appearance of the less noticeable fragments. Copyright © 2005 John Wiley & Sons, Ltd.

The mechanism of the Leuckart reaction of 3,3- and 7,7-dimethyl-2-oxo-1-norbornyl triflates and triflamides, synthesised by us starting from (1R)-camphor and (1R)-fenchone, has been studied. Strikingly, the electron-withdrawing capacity of the bridgehead substituents has demonstrated not to be enough to control the Wagner–Meerwein rearrangement during the course of the reaction, so that only both enantiomers of a 3,3-dimethylnorbornanediamine derivative have been obtained as final products. As a result, the total synthesis of these interesting chiral compounds has been optimised and shortened until three overall steps starting from (1R)-fenchone.

The enantioselective addition of diethylzinc to benzaldehyde has been used as standard procedure to test a series of new chiral catalysts derived from norbornane framework. The new ligands are β-amino alcohols possessing both heteroatomic substituents attached to the C(1) and C(2)-endo positions (novel non-coplanar disposition) of a 3,3-dimethylsubstituted norbornane. The results obtained, compared with other previously reported on the related C(2)-exo-7,7-dimethyl series, demonstrate that the relative disposition of the amino, hydroxy and gem-dimethyl groups, as well as the N-alkyl substituents, play an important role on the catalytic activity. Interesting transition-state models have been also proposed in order to explain the observed experimental results.

The cis/trans ratio of N-methylformamide (NMF), N-methylacetamide (NMA), and N-(2-endo-norbornyl)formamide (NNF) in dilute solutions in chloroform, methanol, and water have been experimentally measured by 1H NMR. Unlike NMA and NMF, the cis/trans ratio of NNF is sensitive to the solvent environment. To understand the anomalous behavior of NNF, we have performed calculations of ΔG and other observables between the cis and trans isomers of NMA, NMF, and NNF both in gas phase and in solution using several ab initio and DFT methods and SCRF models. The strikingly predominance of the trans isomers of N-alkyl substituted formamides can be rationalized in terms of close contact interactions between the formyl group and the C−H bond of the N-alkyl group. The molecular geometries and dipole moments of the studied amides using the RHF and B3LYP theoretical levels and split valence sets are in good accordance with the experimental values. The rotational barriers (ca. 7.0 kcal/mol) around the C2−N bond of cis- and tr...

Five new optically active bridgehead-norbornane-derived β-amino alcohols with different substitution patterns have been obtained using a straightforward procedure from commercial (+)-camphor or (−)-fenchone, and tested as chiral catalysts in the enantioselective diethylzinc-addition to benzaldehyde. The obtained results show that chirality transfer is mainly governed by the hydroxyl group and, therefore, by the surroundings of the CO stereocenter. On the other hand, the N- alkyl substitution play an important role by modulating the degree of enantioselectivity.

Water-soluble gold nanoparticles (3.1±0.6 nm) with polymerization ability and affinity to streptavidin are prepared by reducing HAuCl4 in the presence of the capping ligands 2-mercaptoethanesulfonic acid, biotin–cysteamine, and p-aminothiophenol. This colloid, HAuCl4, is used to modify gold electrodes by forming a 3D electropolymerized network of bis-aniline-cross-linked nanoparticles on the metal surface. The modified electrode is used as a scaffold for the assembly of an amperometric immunosensor system to detect human fibrinogen. The immunosensor shows excellent analytical characteristics, with a dynamic range of detection between 0.018 and 2.208 μg mL−1, a detection limit of 4 ng mL−1, and a half-maximal inhibitory concentration (IC50) of 177 ng mL−1. The immunosensor is markedly stable, retaining full analytical capacity after 45 days of storage at 4 °C.

We report herein the design of a smart delivery system in which cargo delivery from capped mesoporous silica (MS) nanoparticles is controlled by an integrated enzyme-based control unit . The system consists of Janus-type nanoparticles having opposing Au and MS faces, functionalized with a pH-responsive β-cyclodextrin-based supramolecular nanovalve on the MS surface and two effectors, glucose oxidase and esterase, immobilized on the Au face. The nanodevice behaves as an enzymatic logical OR operator which is selectively fueled by the presence of D-glucose and ethyl butyrate., R.V. acknowledges a Ramon & Cajal contract from the Spanish Ministry of Science and Innovation. Financial support from the Spanish Ministry of Science and Innovation (CTQ2011-24355, CTQ2009-12650, CTQ2009-09351, MAT2012-38429-C04-01) and Comunidad de Madrid (S2009/PPQ-1642, programme AVANSENS) is gratefully acknowledged. The Generalitat Valencia (project PROMETEO/2009/016) is also acknowledged.

The electron impact mass spectra of several 3,3-dimethyl-1, 2-norbornanediols, diamines, amino alcohols and related derivatives have been studied and their fragmentation pathways discussed. Different fragmentation patterns were observed, depending not only on the nature of the substituents, but also on their relative positions on the norbornane framework. In general, the dominant peaks in the spectra of these compounds originate from initial C1-C2 bond cleavage (alpha-cleavage) with charge retention on the heteroatom (oxygen or nitrogen) attached at the bridgehead position, followed by hydride shift and loss of the C2-C3 fragment by homolytic cleavage of the C3-C4 bond. This fragmentation pathway leads to a highly stabilized cyclopentenylimmonium or cyclopentenyloxonium ion, which constitutes the base peak in the spectra in most of the studied compounds. Copyright 1999 John Wiley & Sons, Ltd.

Two different 1-amino-3,3-dimethyl-2-methylenenorbornane hydrochlorides, a primary ammonium chloride and a tertiary one, react unexpectedly with m-CPBA (meta-chloroperbenzoic acid) according to two different paths. The primary ammonium chloride gives place to a diastereomeric mixture of the corresponding spiranic 1-nitronorbornane-based epoxides, whereas the tertiary derivative undergoes a skeleton rearrangement giving 10-chlorocamphor. The results are interpreted in terms of competitive reaction pathways controlled by the nitrogenated group located at the C1 norbornane position.

One of the most important features of the synthesis of camphor-derived compounds is the control of the stereochemistry at the C2 position. According to this, reduction of bridgehead-substituted 2-norbornanones 1 and 2-norbornanoximes 3 has been considered by us as a very convenient method for the preparation of different classes of enantiomerically pure 1,2- and 1,3-difunctionalised norbornane derivatives. Factors controlling the stereoselectivity in these reductions, as well as the role played by the nature of the bridgehead functional groups are discussed.

Branched gold nanoparticles were prepared by a seed-mediated approach using per-6-thio-6-deoxy-β-cyclodextrin capped gold nanospheres as seeds and a growth medium similar to those commonly employed to prepare gold nanorods, containing AgNO3, ascorbic acid and cetyltrimethylammonium bromide. Novel jack-shaped gold nanoparticles (102–105 nm) were obtained at a specific range of Ag+ ion concentrations (62–102 μM). The crystalline structure of these nanoparticles was confirmed by high-resolution transmission electron microscopy. The influence of the perthiolated β-cyclodextrin on the successful preparation of gold nanojacks was demonstrated. The jack-shaped gold nanoparticles showed strong absorption in the near infrared region and excellent catalytic activity for the electrochemical oxidation of H2O2. Fil: Sánchez, Alfredo. Universidad Complutense de Madrid; España Fil: Diez, Paula. Universidad Complutense de Madrid; España Fil: Villalonga, Reynaldo. Universidad Complutense de Madrid; España Fil: Martínez Ruiz, Paloma. Universidad Complutense de Madrid; España Fil: Eguilaz Rubio, Marcos. Universidad Complutense de Madrid; España. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Fernandez, Iñigo. Universidad Complutense de Madrid; España Fil: Pingarrón, José M.. Universidad Complutense de Madrid; España

A novel strategy for the construction of disposable amperometric affinity biosensors is described in this work. The approach uses a recombinant bacterial penicillin binding protein (PBP) tagged by an N-terminal hexahistidine tail which was immobilized onto Co2+−tetradentate nitrilotriacetic acid (NTA)-modified screen-printed carbon electrodes (SPCEs). The biosensor was employed for the specific detection and quantification of β-lactam antibiotics residues in milk, which was accomplished by means of a direct competitive assay using a tracer with horseradish peroxidase (HRP) for the enzymatic labeling. The amperometric response measured at −0.20 V versus the Ag pseudoreference electrode of the SPCE upon the addition of H2O2 in the presence of hydroquinone (HQ) as redox mediator was used as the transduction signal. The developed affinity sensor allowed limits of detection to be obtained in the low part-per-billion level for the antibiotics tested in untreated milk samples. Moreover, the biosensor exhibited a good selectivity against other antibiotics residues frequently detected in milk and dairy products. The analysis time was of approximately 30 min., The financial support of the Spanish Ministerio de Economía y Competitividad Research Projects, CTQ2012-34238, and the AVANSENS Program from the Comunidad de Madrid (S2009PPQ-1642) are gratefully acknowledged. Felipe Conzuelo acknowledges an FPU fellowship from the Spanish Ministry of Education.

Janus Au-mesoporous silica nanoparticles were used as scaffolds to design an integrated electrochemical biorecognition-signaling system. A proof of concept of this strategy, based on the face-selective functionalization of the anisotropic colloid, involves the covalent immobilization of horseradish peroxidase on the mesoporous silica face as enzymatic signaling element, as well as the modification of the Au face with streptavidin and polyethylenglycol chains as biorecognition and solubilizing agents, respectively. The functionalized Janus nanoparticles were successful to recognize biotin on gold surfaces. Keywords: Janus nanoparticle, Mesoporous silica, Electrochemical biosensor, Enzyme

Cysteamine core polyamidoamine G-4 dendron branched with β-cyclodextrins was chemisorbed on the surface of Au electrodes and further coated with Pt nanoparticles. Adamantane-modified glucose oxidase was subsequently immobilized on the nanostructured electrode surface by supramolecular association. This enzyme electrode was used to construct a reagentless amperometric biosensor for glucose, making use of the electrochemical oxidation of H2O2 generated in the enzyme reaction. The amperometric response of the biosensor was rapid (6 s) and a linear function of glucose concentration between 5 and 705 μmol L(-1). The biosensor had a low detection limit of 2.0 μmol L(-1), sensitivity of 197 mA mol(-1) L cm(-2), and retained 94% of its initial response after storage for nine days at 4 °C.

The reaction of 2-norbornanones bearing an amine derivative in the bridgehead position with formamide and formic acid yields enantiomerically pure 1,2-norbornane diamides. These compounds are excellent precursors of chiral vicinal diamines, which have been increasingly used due to their numerous applications in medicinal chemistry and asymmetric synthesis. The rigid structure of the norbornane framework allows the study of conformational equilibrium in the formamide groups and its dependence on other substituents in the molecule.

The electron ionisation (EI) mass spectra of a series of bridgehead-fused Delta2-norbornanethiazolines, a new class of bridgehead-norbornane derivatives, have been studied and their cleavage mechanisms rationalised on the basis of the substituent shifts as well as on the identification of relevant peaks through accurate mass measurements and collision-induced dissociation tandem mass spectrometric experiments. The fragmentation patterns of isomeric pairs of 6,6- and 10,10-dimethylnorbornanethiazolines are almost identical, probably due to an initial isomerisation of molecular ion previous to the fragmentation. In general, the dominant peaks in the spectra of all the studied compounds originate from initial alpha-cleavages of C(5)-C(6) or C(1)-C(10) bonds, followed by concomitant homolytic cleavage of C(1)-C(9) and C(7)-C(10) bonds. The driving force for this fragmentation pathway, directed by the gem-dimethyl group, is the formation of a highly stabilised thiazolilmethyl cation which constitutes the base peak in all the spectra and allows the identification of these interesting ligands.

The performance of a molecularly imprinted polymer (MIP) as a selective solid-phase extraction sorbent for the clean-up and preconcentration of the antibiotic chloramphenicol is described. The MIP was prepared using chloramphenicol as the template, (diethylamino)ethyl methacrylate as the functional monomer, and ethylene glycol dimethacrylate as the cross-linking monomer, and using tetrahydrofuran as the solvent. Detection of chloramphenicol was carried out by square-wave voltammetry at electrochemically activated carbon fiber microelectrodes. Chloramphenicol was eluted from the MIP microcolumn with methanol. Different experimental variables (sample pH, eluent volume, analyte and eluent flow rates and sample volume) associated with the rebinding/elution process were optimized. For a 250 mL sample, a nominal enrichment factor of 500 was attained, and for a chloramphenicol concentration of 3.0x10(-8) mol L(-1) (9.7 microg L(-1)) a recovery of 96+/-4% was obtained. A range of linearity for chloramphenicol between 3.0x10(-8) and 1.0x10(-5) mol L(-1) was obtained by loading 17 mL of analyte solutions of different concentration, eluting with 0.5 mL methanol, evaporating under a stream of nitrogen and dissolving the residue in phosphate buffer of pH 7.8. The MIP selectivity was evaluated by checking several substances with similar molecular structures to that of chloramphenicol. The applicability of the MIP for both clean up and preconcentration was demonstrated by determining chloramphenicol in ophthalmic solutions and spiked milk at different concentration levels.

Reduced graphene nanoparticles were prepared from graphene oxide through a two-step covalent modification approach. Graphene oxide was first enriched with reactive epoxy groups by anchoring (3-glycidyloxypropyl)trimethoxysilane at the hydroxyl groups located on the nanocarbon basal plane. Modified graphene oxide was further cross-linked and partially reduced by treatment with the fourth-generation ethylenediamine core polyamidoamine G-4 dendrimer producing graphene nanoparticles with crumpled paper-like morphology. This graphene derivative was employed as a coating material for glassy carbon electrodes and the nanostructured electrode was tested for the preparation of electrochemical biosensors by immobilizing the enzyme tyrosinase through cross-linking with glutaraldehyde. This bioelectrode showed excellent electroanalytical behavior for catechol with a fast response in about 6 s, linear range of 10 nM to 22 μM, sensitivity of 424 mA M−1, and low detection limit of 6 nM. The enzyme biosensor also showed high stability when stored at 4 °C under dry and wet conditions.

The single-point total energy (E) of several acyclic and cyclic oligomers of N-methylformamide (NMF) was computed by the first time without any geometrical restriction, using the B3LYP6-31G* method of the density functional theory in order to determine the effect of self-association on intramolecular geometrical parameters of cis- and trans-NMF, the intermolecular distances of the hydrogen-bonding chains formed by NMF as well as intermolecular association energies including counterpoise corrections. It is concluded that liquid NMF exists mainly as polymers formed by self-association of trans-NMF units, whereas the cis-NMF isomer occurs as isolated units inserted along the chains. These computational results are in accordance with the experimentally determined predominance (ca. 90%) of trans-NMF population by means of (1)H- NMR and other spectroscopic techniques, but in severe contradiction with a recent interpretation of x-ray diffraction data on liquid NMF, postulating a cyclic trimer of cis-NMF (c-C(3)) as the predominating species. The counterpoise-corrected values of the association energy, DeltaE(CP), calculated for cyclic oligomers, increase with the polymerization degree (n) revealing a high grade of cooperative effect for amidic hydrogen-bonded chains. Noteworthy, the difference between the DeltaE(CP) values of the cyclic cis- and trans-homooligomers of NMF is positive for n=2 and 3 but negative for nor =4.

The synthesis of chiral amine norbornane derivatives has been achieved by means of the Leuckart reaction of various 2-norbornanones. We propose an ionic mechanism for this process in which the formation of a 2-formylamino-2-norbornyl cation is the common initial step. The reaction pathway and the isolated products are strongly dependent on the nature of the bridgehead substituents; hydrogen and alkyl groups yield only enantiopure 2-norbornyl formamides with structural retention, whereas O-acyl or N-acyl groups favour a pinacol-type skeleton rearrangement through a cascade of Wagner−Meerwein rearrangements and intramolecular transamidations.