Norcamphor

Zn-Catalyzed Multicomponent KA(2) Coupling: One-Pot Assembly of Propargylamines Bearing Tetrasubstituted Carbon Centers.[Pubmed:31460120]

ACS Omega. 2019 Jun 13;4(6):10279-10292.

Tetrasubstituted propargylamines comprise a unique class of highly useful compounds, which can be accessed through the multicomponent coupling between ketones, amines, and alkynes (KA(2) coupling), an underexplored transformation. Herein, the development of a novel, highly efficient, and user-friendly catalytic system for the KA(2) coupling, based on the environmentally benign, inexpensive, and readily available zinc acetate, is described. This system is employed in the multicomponent assembly of unprecedented, tetrasubstituted propargylamines derived from structurally diverse, challenging, and even biorelevant substrates. Notable features of this protocol include the demonstration of the enhancing effect that neat conditions can have on catalytic activity, as well as the expedient functionalization of hindered, prochiral cyclohexanones, linear ketones, and interesting molecular scaffolds such as Norcamphor and nornicotine.

Biocatalysis for terpene-based polymers.[Pubmed:30789828]

Z Naturforsch C J Biosci. 2019 Feb 25;74(3-4):91-100.

Accelerated generation of bio-based materials is vital to replace current synthetic polymers obtained from petroleum with more sustainable options. However, many building blocks available from renewable resources mainly contain unreactive carbon-carbon bonds, which obstructs their efficient polymerization. Herein, we highlight the potential of applying biocatalysis to afford tailored functionalization of the inert carbocyclic core of multicyclic terpenes toward advanced materials. As a showcase, we unlock the inherent monomer reactivity of Norcamphor, a bicyclic ketone used as a monoterpene model system in this study, to afford polyesters with unprecedented backbones. The efficiencies of the chemical and enzymatic Baeyer-Villiger transformation in generating key lactone intermediates are compared. The concepts discussed herein are widely applicable for the valorization of terpenes and other cyclic building blocks using chemoenzymatic strategies.

Asymmetric [4+2] annulations to construct norcamphor scaffolds with 2-cyclopentenone via double amine-thiol catalysis.[Pubmed:29334089]

Chem Commun (Camb). 2018 Jan 25;54(9):1129-1132.

An efficient double catalytic system, combining chiral amine and 2-mercaptobenzoic acid, is applied for alpha',beta-regioselective [4+2] annulations of 2-cyclopentenone with a diversity of activated alkenes, constructing multifunctional chiral bicycle[2,2,1]heptane scaffolds in good to excellent yields and enantioselectivities. In comparison with the traditional cross-dienamine species between 2-cyclopentenone and chiral amine, the interrupted enamine intermediate containing a covalently linked thiol catalyst shows significantly improved reactivity.

Direct Access to Multifunctionalized Norcamphor Scaffolds by Asymmetric Organocatalytic Diels-Alder Reactions.[Pubmed:26457897]

Angew Chem Int Ed Engl. 2015 Nov 9;54(46):13630-4.

A general organocatalytic cross-dienamine activation strategy to produce chiral multifunctionalized Norcamphor compounds having a large diversity in substitution pattern is presented. The strategy is based on a Diels-Alder reaction of an amino-activated cyclopentenone reacting with most common classes of electron-deficient olefins, such as nitro-, ester-, amide-, and cyano-substituted olefins, chalcones, conjugated malononitriles, CF3-substituted enones, and fumarates. The corresponding Norcamphor derivatives are formed in good yield, excellent enantioselectivities, and with complete diastereoselectivity. Furthermore, it is demonstrated that quaternary stereocenters and spiro Norcamphor compounds can be formed with high stereoselectivity. The present development provides a simple, direct, and efficient approach for the preparation of important Norcamphor scaffolds.

Conformational landscape and the selectivity of cytochrome P450cam.[Pubmed:25955684]

J Phys Chem B. 2015 Jun 4;119(22):6620-7.

Conformational heterogeneity and dynamics likely contribute to the remarkable activity of enzymes but are challenging to characterize experimentally. These features are of particular interest within the cytochrome P450 class of monooxygenases, which are of great academic, medicinal, and biotechnological interest as they recognize a broad range of substrates, such as various lipids, steroid precursors, and xenobiotics, including therapeutics. Here, we use linear and 2D IR spectroscopy to characterize the prototypical P450, cytochrome P450cam, bound to three different substrates, camphor, Norcamphor, or thiocamphor, which are hydroxylated with high, low, and intermediate regioselectivity, respectively. The data suggest that specific interactions with the substrate drive the population of two different conformations, one that is associated with high regioselectivity and another associated with lower regioselectivity. Although Y96 mediates a hydrogen bond thought necessary to orient the substrate for high regioselectivity, the population and dynamics of the conformational states are largely unaltered by the Y96F mutation. This study suggests that knowledge of the conformational landscape is central to understanding P450 activity, which has important practical ramifications for the design of therapeutics with optimized pharmacokinetics, and the manipulation of P450s, and possibly other enzymes, for biotechnological applications.

Tautomerization-mediated molecular switching between six- and seven-membered rings stabilized by hydrogen bonding.[Pubmed:25940593]

Chemistry. 2015 Jun 8;21(24):8939-45.

1,3,4,6-Tetraketones typically undergo keto-enol tautomerism forming bis-enols stabilized by intramolecular hydrogen bonding in two six-membered rings. However, 1,3,4,6-tetraketones derived from the terpene ketone camphor and Norcamphor exist as isomers with two distinguishable modes of intramolecular hydrogen bonding, namely, the formation of six- or seven-membered rings. The structural requirements for this so far unknown behavior were investigated in detail by synthesis and comparison of structural analogues. Both isomers of such 1,3,4,6-tetraketones were fully characterized in solution and in the solid state. Intriguingly, they slowly interconvert in solution by means of tautomerism-rotation cascades, as was corroborated by DFT calculations. The influence of temperature and complexation with the transition metals Pd, Rh, and Ir on the interconversion process was investigated.

Photoelectron circular dichroism of bicyclic ketones from multiphoton ionization with femtosecond laser pulses.[Pubmed:25492564]

Chemphyschem. 2015 Jan 12;16(1):115-37.

Photoelectron circular dichroism (PECD) is a CD effect up to the ten-percent regime and shows contributions from higher-order Legendre polynomials when multiphoton ionization is compared to single-photon ionization. We give a full account of our experimental methodology for measuring the multiphoton PECD and derive quantitative measures that we apply on camphor, fenchone and Norcamphor. Different modulations and amplitudes of the contributing Legendre polynomials are observed despite the similarity in chemical structure. In addition, we study PECD for elliptically polarized light employing tomographic reconstruction methods. Intensity studies reveal dissociative ionization as the origin of the observed PECD effect, whereas ionization of the intermediate resonance is dominating the signal. As a perspective, we suggest to make use of our tomographic data as an experimental basis for a complete photoionization experiment and give a prospect of PECD as an analytic tool.

Toxicity Studies on Novel N-Substituted Bicyclo-Heptan-2-Amines at NMDA Receptors.[Pubmed:24276123]

Pharmaceuticals (Basel). 2013 Apr 12;6(4):536-45.

Several novel Norcamphor derivatives were designed and synthesized as uncompetitive NMDA receptor antagonists at the phencyclidine (PCP) binding site. Such compounds have potential as ligands for understanding and possibly the treatment of several neurodegenerative disorders and other glutamate-dependent disorders. We examined the toxic effects of the compounds as compared with memantine, an NMDA receptor antagonist that is FDA approved for treatment of Alzheimer's disease, by testing these compounds on two cell lines: MDCK (to mimic blood brain barrier) and N2a (a neuronal cell line). The compounds showed toxicity profiles similar to those of memantine i.e., dose dependence above 100 muM and IC50 values above 150 muM for each cell line. It is known that the serum level of memantine under therapeutic conditions in patients is about 1 microM, indicting these compounds could have acceptable therapeutic indexes. 2-Phenyl-N-(2-(piperidin-1-yl) ethyl)bicyclo[2.2.1]heptan-2-amine (5a) was found to possess acceptable toxicity profiles in both cell lines. Interestingly, this was the compound identified as a good lead in our previous studies based on binding and anticonvulsant (MES) activity studies. It has thus emerged as an excellent lead compound for further studies.

Functional assembly of camphor converting two-component Baeyer-Villiger monooxygenases with a flavin reductase from E. coli.[Pubmed:24190498]

Appl Microbiol Biotechnol. 2014 May;98(9):3975-86.

The major limitation in the synthetic application of two-component Baeyer-Villiger monooxygenases was addressed by identifying the 28-kDa flavin-reductase Fre from Escherichia coli as a suitable supplier of reduced FMN for these enzymes. Coexpression of Fre with either 2,5- or 3,6-diketocamphane monooxygenase from Pseudomonas putida NCIMB 10007 significantly enhanced the conversion of camphor and Norcamphor serving as representative ketones. With purified enzymes, full conversion was achieved, while only slight amounts of product were formed in the absence of this flavin reductase. Fusion of the genes of Fre and DKCMOs into single open reading frame constructs resulted in unstable proteins exhibiting flavin reducing, but poor oxygenating activity, which led to overall decreased conversion of camphor.

Noncovalently and covalently cross-linked polyurethane gels as alignment media and the suppression of residual polymer signals using diffusion-filtered spectroscopy.[Pubmed:23280657]

Magn Reson Chem. 2012 Dec;50 Suppl 1:S22-8.

With polyurethane (PU), a novel alignment medium for organic solvents is introduced and characterized, which is very robust and easy to produce on a large scale. Linear PU already constitutes an elastomer gel with several solvents based on its ability to form hydrogen bonds. Covalent cross-linking of the polymer with accelerated electrons provides an alignment medium with different properties. However, PU exhibits a number of undesired polymer signals in corresponding spectra, which ideally have to be removed spectroscopically. Within this context, we demonstrate the applicability of diffusion-filtered experiments for removal of the polymer signals. Example spectra for the usefulness of PU alignment media are provided for the common test molecules strychnine and Norcamphor.

Dual action spirobicycloimidazolidine-2,4-diones: antidiabetic agents and inhibitors of aldose reductase-an enzyme involved in diabetic complications.[Pubmed:23246355]

Bioorg Med Chem Lett. 2013 Jan 15;23(2):488-91.

The desired 3-(arylsulfonyl)spiroimidazolidine-2,4-diones were synthesized by reacting spiroiminoimidazolidine-2,4-dione with arylsulfonyl chlorides. Spiroimidazolidine-2,4-dione was in turn synthesized from Norcamphor. Structures of the synthesized molecules were established by modern spectroscopic techniques. The synthesized compounds were screened for in vivo antidiabetic activity and aldose reductase inhibition. Compounds 2a, 2b and 2g exhibited excellent dual activity, compound 2a being most prominent. These results reveal that the synthesized compounds may serve as the molecule of choice to treat diabetes and diabetic complications using a single medication.

Completing the series of BVMOs involved in camphor metabolism of Pseudomonas putida NCIMB 10007 by identification of the two missing genes, their functional expression in E. coli, and biochemical characterization.[Pubmed:22286514]

Appl Microbiol Biotechnol. 2012 Oct;96(2):419-29.

The camphor-degrading Baeyer-Villiger monooxygenases (BVMOs) from Pseudomonas putida NCIMB 10007 have been of interest for over 40 years. So far the FMN- and NADH-dependent type II BVMO 3,6-diketocamphane 1,6-monooxygenase (3,6-DKCMO) and the FAD- and NADPH-dependent type I BVMO 2-oxo-3-4,5,5-trimethylcyclopentenylacetyl-CoA monooxygenase (OTEMO) have not been entirely studied, since it was not possible to produce those enzymes in satisfactory amounts and purity. In this study, we were able to clone and recombinantly express both enzymes and subsequently use them as biocatalysts for various mono- and bicyclic ketones. Full conversion could be reached with both enzymes towards (+/-)-cis-bicyclo[3.2.0]hept-2-en-6-one and with 3,6-DKCMO towards (-)-camphor. Further OTEMO gave full conversion with Norcamphor. OTEMO was found to have a pH optimum of 9 and a temperature optimum of 20 degrees C and converted (+/-)-cis-bicyclo[3.2.0]hept-2-en-6-one with a k cat/K M value of 49.3 mM-1 s-1.

An automated microscale platform for evaluation and optimization of oxidative bioconversion processes.[Pubmed:22223589]

Biotechnol Prog. 2012 Mar-Apr;28(2):392-405.

In this work an integrated robotic platform has been used for the development of a fully automated microscale process sequence comprising fermentation and bioconversion using E. coli TOP10 [pQR210] expressing cyclohexanone monooxygenase (CHMO). Ninety six-Deep Square Well (96-DSW) microtiter plates were used for microbial culture and enzyme-catalyzed conversion, where plate preparation, reagent addition, and sampling were all carried out without manual intervention. The adoption of automated robotic procedures has enabled the rapid collection of kinetic data for whole process optimization at the microscale. This high-throughput approach enabled a range of amino acid sources for media formulation and well fill volumes to be investigated highlighting when nutritional limitation and oxygen limitations took place. The automated process sequence has been applied to test six CHMO substrates including Norcamphor and cycloheptanone all of which to the best of our knowledge have yet to be tested with E. coli TOP10 [pQR210]. Substrate specificity and product selectivity were effectively demonstrated and compared to both the natural substrate cyclohexanone and the model substrate bicyclo[3.2.0]hept-2-en-6-one used to demonstrate asymmetric synthesis. The results obtained using the developed process sequence could be reproduced at 75 L scale when a matched oxygen transfer coefficient k(L) a approach was used. The study demonstrates how automated microscale processing enables the rapid collection of kinetic quantitative data in a robust manner with clear implications for accelerating bioprocess development, optimization, and scale-up.

Time-dependent fifth-order bands in nominally third-order 2D IR vibrational echo spectra.[Pubmed:21648438]

J Phys Chem A. 2011 Sep 1;115(34):9714-23.

Progress in the field of 2D IR vibrational spectroscopy has been bolstered by the production of intense mid-IR laser pulses. As higher-energy pulses are employed, a concomitant increase occurs in the likelihood of fifth-order contributions to the 2D IR spectra. We report the appearance of fifth-order signals in 2D IR spectra of CO bound to the active site of the enzyme cytochrome P450(cam) with the substrate Norcamphor. Two bands with novel time dependences, one on the diagonal and one off-diagonal, are not accounted for by normal third-order interactions. These bands are associated with a nu = 1-2 vibrational transition frequency. Both bands decay to 0 and then grow back in with opposite sign. The diagonal band is positive at short time, decays to 0, reappears with negative sign, before eventually decaying to 0. The off-diagonal band is negative at short time, decays to 0, reappears positive, and then decays to 0. The appearance and time dependence of these bands are characterized. Understanding these fifth-order bands is useful because they may be misidentified with time-dependent bands that arise from other processes, such as chemical exchange, vibrational coupling, or energy transfer. The presence and unusual time dependences of the fifth-order bands are reproduced with model calculations that account for the fact that vibrational relaxation from the nu = 2 to 1 level is approximately a factor of 2 faster than that from the nu = 1 to 0 level.

Syntheses and pharmacological evaluations of novel N-substituted bicyclo-heptane-2-amines at N-methyl-D-aspartate receptors.[Pubmed:21496213]

Chem Biol Drug Des. 2011 Jul;78(1):25-32.

Several novel Norcamphor (bicycloheptane)-based compounds were designed and synthesized as non-competitive N-methyl-D-aspartate receptor antagonists at the phencyclidine binding sites. The heterocyclic ring was also varied to examine piperidine, pyrrolidine, and morpholine groups. We examined pharmacological activities of these compounds in vitro (binding studies) and in vivo (maximal electroshock test). Pharmacological evaluations revealed one of the compounds, 5a, to be a good lead, exhibiting moderate binding at N-methyl-D-aspartate receptors (IC(50) =7.86 mum; K(i) =5.28 mum), maximal electroshock neuroprotection activity at 100 mg/kg and acceptable toxicity profile.