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41 Aerobic C-N Bond Formation via Enzymatic Nitroso Ene Reactions
C. Jäger, J. Deska, 2020, submitted
The direct allylic nitrogen functionalization is a rare domain in biocatalysis. Imitating traditional metal catalysis, a very first enzyme mediated ene-type reaction involving intermediate acylnitroso compounds enhances the selection of the organochemical toolbox. Offering two possibilities, exploiting copper based laccases as oxidizing catalyst or an interplay of commercial horseradish peroxidase as oxygen-activating catalyst and wild-type chloroperoxidase as oxygen-transfer mediator, a selective oxidation of NOH moieties was found. Mechanistic studies uncovered an inverse β secondary isotope effect indicating an aziridine N-oxide as intermediate in the rate-limiting step. The absence of any primary kinetic isotope effects revealed a stepwise mechanism with irreversible formation of an intermediate.
The one-pot combination of halogenation biocatalysis and Suzuki-type cross coupling enables the direct arylative cyclization of allenic alcohols with boronic acids. This modular approach to unsaturated five-membered O-heterocycles proceeds in an aqueous emulsion with air as terminal oxidant. Here, the enzymatic oxidative activation of simple halide salts acts as traceless ring-closure-inducing event to trigger the subsequent C‑C coupling. With the original protocol merging soluble proteins and a homogeneous SPhos-based palladium catalyst as a template, a novel heterogeneous nanobiohybrid was developed. Consisting of an oxidase matrix hosting small spherical palladium nanoparticles, this enzyme-metal hybrid exhibits catalytic competence for both the biocyclization as well as the C‑C bond-forming cross coupling, underlining the potential of this new techniques for streamlining chemoenzymatic approaches.
40 Arylative Allene Cyclization by Sequential Enzyme & Palladium Catalysis
J. M. Naapuri, J. M. Palomo, G. Åberg, J. Deska, 2020, submitted
39 A Kirmse Mutase – Copper Proteins Catalyse [2,3]-Sigmatropic Oxonium Ylide Rearrangements
F. Blume, F. Mollerup, M. Sandgren, E. Master, J. Deska, 2020, manuscript in preparation
Sugar-degrading copper-dependent oxidoreductases serve as effective initiator for the Kirmse-Doyle-type sigmatropic rearrangement of allylic and propargylic oxonium ylides in water yielding functionalized and stereochemically defined tetrahydrofuran building blocks.
38 Anti-angiogenic and anti-inflammatory activity of the truffle 'Tuber aestivum' extracts and a correlation with the chemical constituents identified therein
S. J. Marathe, W. Hamzi, A. M. Bashein, J. Deska, T. Seppänen-Laakso, R S. Singhal, S. Shamekh
Food Res. Int. 2020, accepted
Fungi are a very rich source of untouched bioactive compounds. Owing to their biological activities, several fungi have shown commercial application in the health industry. Tuber aestivum is one such fungi with an immense potential for practical biological application. In the present study, the anti-angiogenic activity of petroleum ether and ethanol extracts of T. aestivum was investigated using the chick chorioallantoic membrane assay and compared to the positive controls silibinin and lenalidomide. Both extracts showed a dose-dependent anti-angiogenic response. The extracts were also assessed for their anti-inflammatory potential through a lipoxygenase-inhibition assay. The IC50 values in LOX inhibition assay, computed by the Boltzmann plot, were 368.5, 147.3 and 40.2 µg/mL, for the petroleum ether, ethanol extracts, and the positive control ascorbic acid, respectively. In direct comparison, the ethanol extract of T. aestivum showed superior anti-angiogenic and anti-inflammatory activity than the petroleum ether extract. Compositional investigation of the extracts was performed using GC-MS analysis and revealed the presence of various bioactive compounds. The compounds were correlated to their anti-angiogenic and anti-inflammatory activity based on a meticulous literature search.
37 In silico characterization of bacterial chitinase: illuminating the evolutionary relationship with archeal and
B. Datta, J. Deska, R. Bandopadhyay, S. Shamekh
Comp. Biol. Chem. 2020, under revision
Chitin is one of the most abundant biopolymers on Earth, only trailing second after cellulose. The enzyme chitinase is responsible for the degradation of chitin. Chitinases are found to be produced by wide range of organisms ranging from archea to higher plants. Though chitin is a major component of fungal cell walls and invertebrate exoskeleton, bacterialchitinase can be industrially generated at low cost, in facile downstream processes at high production rate.Microbial chitinases are more stable, active and economically practicable compared to the plant and animal derived enzymes. In the present study, we have worked upon the Chitinase, emphasizing of bacterial origin which is fulfilling all the required quality needed to be a commercial production. 62 Chitinase sequences from four different group of organisms are collected from RCSB PDB. Considering one suitable sequence from each group is being compared with others. Primary, secondary and tertiary structures are determined by in silicomodels. Different physical parameters viz., pI, molecular weight, instability index, aliphatic index, GRAVY, presence of functional motifs are determined. Phylogenetic tree has been constructed to find out the relationship with other group of organisms. These provides insight into distribution of chitinase and further characterization and industrial assessment of the desired enzyme.
36 Biocatalytic production of amino-carbohydrates through oxidoreductase and transaminase cascades
V. Aumala, F. Mollerup, E. Jurak, F. Blume, J. Karppi, A. E. Koistinen, E. Schuiten, M. Voß, U. T. Bornscheuer, J. Deska, E. R. Master
ChemSusChem 2019, in print
Plant-derived carbohydrates constitute an abundant renewable resource. Transformation of carbohydrates into new products, including amine-functionalized building blocks for biomaterial applications, can lower reliance on fossil resources. Herein, we demonstrate biocatalytic production routes to amino-carbohydrates, including oligosaccharides. In each case, we performed a two-step biocatalysis to functionalized D-galactose-containing carbohydrates, which employed either the galactose oxidase from Fusarium graminearum or a pyranose dehydrogenase from Agaricus bisporus followed by the w-transaminase from Chromobacterium violaceum (Cvi-w-TA). Formation of 6-amino-6-deoxy-d-galactose, 2-amino-2-deoxy-d-galactose and 2-amino-2-deoxy-6-aldo-d-galactose
was confirmed by mass spectrometry. Cvi-w-TA activity was highest towards 6-aldo-d-galactose and xyloglucan oligosaccharides, where highest yield of 6-amino-6-deoxy-d-galactose from d-galactose (60%) was achieved in reactions permitting simultaneous oxidation of d-galactose and transamination of the resulting 6-aldo-d-galactose. .
35 Chemoenzymatic Hydrogen Production from Methanol Through the Interplay of Metal Complexes and Biocatalysts
G. Tavakoli, J. E. Armstrong, J. M. Naapuri, J. Deska*, M. H. G. Prechtl*, Chem. Eur. J. 2019, 25, doi:10.1002/chem.201806351
Bacterial methylotrophic organisms can serve as great inspiration in the development of biomimetic interconversion of C1 molecules at ambient conditions. In this concept article, we give a brief personal perspective on the recent advancement in the field of biomimetic catalytic interconversion of methanol and formaldehyde in presence and absence of enzymes and co-factors towards the formation of hydrogen at ambient conditions. In particular organometallic formaldehyde dehydrogenase and dismutase mimics have been introduced in standalone C1-interconversion networks. Also, coupled systems with alcohol oxidase and dehydrogenase enzymes for the in situ formation and decomposition of formaldehyde and/or NADH/NAD+ have been developed in recent years. These conceptual bio-inspired low-temperature energy conversion processes may lead one day to more efficient energy storage systems enabling hydrogen generation for hydrogen fuel cells at ambient conditions using C1 molecules as fuels.
34 Shape and Phase Transitions in a PEGylated Phospholipid System
L. Viitala, S. Pajari, L. Gentile, J. Määttä, M. Gubitosi, J. Deska, M. Sammalkorpi, U. Olsson, L. Murtomäki
Langmuir 2019, doi:10.1021/acs.langmuir.2018-03829v (in print)
Poly(ethylene glycol) (PEG) polymers and PEG-conjugated lipids are widely used in bioengineering and drug transport applications. The PEG layer increases hydrophilic repulsion, inhibits membrane fusion and serum opsonin interactions, and prolongs the storage and circulation times, but it can also change the carrier shape and have influence to many content-release-related properties. In this paper, we focus on the physicochemical effects of PEGylation in the lipid bilayer. We use cryo-TEM, DSC, molecular dynamics (MD) simulations, fluorescence spectroscopy of laurdanC, and SAXS/WAXS to acquire information of the particle/bilayer morphology and phase behavior in systems containing DPPC:DSPE-PEG(2000) with different fractions. We show that there are two regions of interest that could be used to improve PEGylated lipid applications. The first one involves spherical vesicles and a window of elevated chain melting temperatures that could be utilized in targets requiring multiple release sequences. The other region is the liposome-to-bicelle transition that is indirectly controlled by the polymer size. This important finding could be used to achieve more efficient drug release and to control other smart materials.
Alcohol dehydrogenases can act as powerful catalysts in the preparation of optically pure gamma-hydroxy-delta-lactones by means of an enantioconvergent dynamic redoxisomerization of readily available Achmatowicz-type pyranones. Imitating the traditionally metal-mediated borrowing hydrogen approach to shuffle hydrides across molecular architectures and interconvert functional groups, this chemoinspired and purely biocatalytic interpretation effectively expands the enzymatic toolbox and provides new opportunities in the assembly of multi-enzyme cascades and tailor-made cellular factories.
33 Biocatalytic Enantioconvergent Redoxisomerization
Y.-C. Liu, C. Merten, J. Deska,
Angew. Chem. Int. Ed. 2018, 57, 12151-12156
Angew. Chem. 2018, 130, 12328-12333
32 Kirmse-Doyle- and Stevens-type Rearrangements of Glutarate-derived Oxonium Ylides
B. Skrobo, N. E. Schlörer, J.-M. Neudörfl, J. Deska
Chem. Eur. J. 2018, 24, 3209-3217
A novel chemoenzymatic synthetic cascade enables the preparation of densely decorated tetrahydrofuran building blocks. Here, the lipase-catalyzed desymmetrization of 3-alkoxyglutarates renders highly enantioenriched carboxylic acid intermediates, whose subsequent activation and oxonium ylide rearrangement by means of rhodium or copper complexes furnishes functionalized O-heterocycles with excellent diastereoselectivity. The two-step protocol offers a streamlined and flexible synthesis of tetrahydrofuranones bearing different benzylic, allylic or allenylic side chains with full control over up to three stereogenic centers.
31 Chloroperoxidase-catalyzed Achmatowicz Rearrangements
D. Thiel, F. Blume, C. Jäger, J. Deska
Eur. J. Org. Chem. 2018, 20, 2717-2725.
Chloroperoxidase from Caldariomyces fumago catalyzes the selective oxidation of furfuryl alcohols in an Achmatowicz-type ring expansion. In combination with glucose oxidase as oxygen-activating biocatalyst, a purely enzymatic, aerobic protocol for the synthesis of 6-hydroxypyranone building blocks is obtained. Thanks to an only modest stereochemical bias of the oxygenating heme protein, optically active alcohols of either configuration are converted without a significant mismatch opening up opportunities for enantioselective multienzymatic cascades. Balancing the oxidase-driven aerobic activation, extended enzyme half-lifes and productive conversion of poorly soluble and slowly reacting substrates can be achieved with high yields of the six-membered O‑heterocycles.
30 Lipase-induced Oxidative Furan Rearrangements
F. Blume, P. Sprengart, J. Deska
Synlett 2018, 29, 1293-1296
Lipase B from Candida antarctica catalyzes the oxidative ring expansion of furfuryl alcohols using aqueous hydrogen peroxide to yield functionalized pyranones under mild conditions. The method further allows for the preparation of corresponding piperidinone architectures by enzymatic rearrangement of N-protected furfurylamines.
29 Fermentative production of extracellular amylase from novel amylase producer, Tuber maculatum mycelium
D. K. Bedade, R. S. Singhal, S. Bankar, S. Bejar, J. Deska, S. Shamekh
Prep. Biochem. Biotechnol. 2018, 48, doi: 10.1080/10826068.2018.1478976
Truffles are symbiotic hypogeous edible fungi that form filamentous mycelia in their initial phase of the growth cycle as well as a symbiotic association with host plant roots. In this study, Tuber maculatum mycelia were isolated and tested for extracellular amylase production at different pH on solid agar medium. Furthermore, the mycelium was subjected to submerged fermentation for amylase production under different culture conditions such as variable carbon sources and their concentrations, initial medium pH, and incubation time. The optimized conditions after the experiments included soluble starch (0.5% w/v), initial medium pH of 7.0, and incubation time of 7 days, at room temperature (22 ± 2 °C) under static conditions which resulted in 1.40 U/mL of amylase. The amylase thus obtained was further characterized for its biocatalytic properties and found to have an optimum activity at pH 5.0 and at a temperature of 50 °C. The enzyme showed good thermostability at 50 °C by retaining 98 % of the maximal activity after 100 min of incubation. The amylase's performance was enhanced in presence of Cu2+ additives and slightly reduced by K+, Ca2+, Fe2+, Mg2+, Co2+, Zn2+, and Mn2+ ions at 1 mM concentration.
28 Enzymatic Halocyclization of Allenic Alcohols & Carboxylates: A Biocatalytic Entry to Functionalized O-Heterocycles
J. Naapuri, J. D. Rolfes, J. Keil, C. Manzuna Sapu, J. Deska
Green Chem. 2017, 19, 447-452.
Chloroperoxidase from Caldariomyces fumago catalyzes the aerobic oxidative halocyclization of allenic alcohols and carboxylates yielding functionalized furan and pyran heterocycles as valuable synthetic scaffolds. Thanks to an oxidase-initiated redox cascade, simple halide salts – in combination with air and glucose – act as stoichiometric reagents for the in situ generation of reactive halonium species. Under the mild reaction conditions in an aqueous emulsion medium, the stereochemical integrity of diastereo- and enantioenriched allenes remains uncompromised and chiral dihydrofurans can be obtained via 5-endo-trig cyclizations with perfect axis-to-centre chirality transfer.
27 Extracellular Xylanase Production from a New Xylanase Producer Tuber maculatum Mycelium under Submerged Fermentation and its Characterization
D. K. Bedade, O. Berezina, R. Singhal, J. Deska, S. Shamekh
Biocatal. Agric. Biotechnol. 2017, 11, 288-293.
Truffles are edible fungi that grow symbiotically with several trees. In this study, Tuber maculatum mycelia were isolated and screen qualitatively for extracellular xylanase production at a broad pH range (4.0, 7.0 and 9.0) in agar plates. Based on zone of clearance highest xylanase activity was observed at pH 7.0. Furthermore, T. maculatum mycelium was studied for effect of various carbon sources, initial medium pH, agitation and fermentation time on xylanase production in submerged fermentation. Under optimized conditions maximum xylanase activity (13.15 U/mL) was detected after 6 days of fermentation at static condition in the basal salt medium with the initial medium pH of 7.0 and 0.5% xylan. The xylanase showed maximum activity at 50 °C and pH 5.0. The Zn2+ activated the xylanase but Co2+ was found inhibitory towards the same. The results indicated that truffle mycelium is utilizing xylan as energy source from host plant root system.
26 Biochemical Characterization of Extracellular Cellulase from Tuber maculatum mycelium produced under submerged fermentation
D. K. Bedade, O. Turunen, J. Deska, S. Shamekh
Appl. Biochem. Biotechnol. 2017, 181, 772-783.
Interaction of truffle mycelium with the host plant involves the excretion of extracellular enzymes. Tuber maculatum mycelia were isolated and tested for extracellular cellulase production at variable pH (4.0, 7.0 & 9.0) on solid agar medium, and the highest activity was observed at pH 7.0. Furthermore, T. maculatum was subjected to submerged fermentation in basal salt medium for cellulase production. Under optimized conditions using sodium carboxymethyl cellulose (0.5% w/v) as carbon source and an initial pH of 7.0, the enzyme production yielded 1.70 U/ml of cellulase in the cell-free cultural liquid after seven days of incubation time. The optimum of the obtained cellulase's activity was at pH 5.0 and a temperature of 50 °C. The enzyme showed good thermostability at 50 °C by retaining 99 % of its maximal activity over an icubation time of 100 min. The cellulase activity was inhibited by Fe2+ and slightly activated by Mn2+ and Cu2+ at 1 mM concentration. The results indicated that truffle mycelium is utilizing cellulosic energy source in the root system and the optimal conditions are those existing in the acidic Finnish soil.
25 An Organometallic Dismutase – Self-Sufficient Formaldehyde-to-Methanol Conversion
D. van der Waals, L. E. Heim, S. Vallazza, C. Gedig, J. Deska, M. H. G. Prechtl
Chem. Eur. J. 2016, 22, 11568-11573.
The catalytic networks of methylotrophic organisms featuring redox enzymes for the activation of one-carbon moieties can serve as great inspiration in the development of novel homogeneously catalysed pathways for the interconversion of C1 molecules at ambient conditions. An imidazolium-tagged arene-ruthenium complex was identified as an effective functional mimic of bacterial formaldehyde dismutase that provides a novel and highly selective route for the conversion of formaldehyde to methanol in absence of any external reducing agents. Moreover, secondary amines are reductively methylated by the organometallic dismutase mimic in a redox self-sufficient manner with formaldehyde acting both as carbon source and reducing agent.
24 Chemoenzymatic Total Synthesis of (+)- & (−)-cis-Osmundalactone
F. Blume, Y. C. Liu, D. Thiel, J. Deska
J. Mol. Catal. B Enzym. 2016, 134, 280-284.
Both optical antipodes of the cis-isomers of osmundalactone, a hydroxypyranone natural product and core structure of the angiopterlactones, have been synthesized from acetylfuran in only three steps through a redox cascade utilizing oxidoreductases and transition metal catalysis in a concerted fashion. The key step in this fully catalytic strategy is the enzyme-mediated Achmatowicz reaction via selective furan oxygenation to furnish the pyran core structure.
23 Enzymatic Approaches for the Preparation of Optically Active Non-Centrochiral Compounds
B. Skrobo, J. D. Rolfes, J. Deska
Tetrahedron. 2016, 72, 1257-1275. Link
This report provides a full summary over all activites exploiting biocatalysis for the synthesis of enantioenriched axially, planarly, and helically chiral molecules over the past four decades. Introducing the basic activation modes of the most frequently employed enzyme classes, this review will highlight the power of biocatalysis – ranging from classical whole-cell systems to contemporary tailor-made proteins – to effectively act on highly non-natural substrate structures in a synthetic fashion.
22 Bioinduced Room Temperature Methanol Reforming
L. E. Heim, D. Thiel, C. Gedig, J. Deska,* M. H. G. Prechtl*
Imitating Nature's approach in nucleophile-activated formaldehyde dehydrogenation, air stable ruthenium complexes proved to be exquisite catalysts for the dehydrogenation of formaldehyde hydrate as well as for the transfer hydrogenation to unsaturated organic substrates at loadings as low as 0.5 mol%. Concatenation of the chemical hydrogen fixation route with an oxidase-mediated activation of methanol renders an artificial methylotrophic in vitro metabolism providing methanol-derived reduction equivalents for synthetic hydrogenation purposes. Moreover, for the first time methanol reforming at room temperature was achieved on the basis of this bioinduced dehydrogenation path delivering hydrogen gas from aqueous methanol.
21 The Achmatowicz Rearrangement: Oxidative Ring Expansion of Furfuryl Alcohols (review)
J. Deska, D. Thiel, E. Gianolio
Synthesis 2015, 47, 3435-3450. Link
Over the years, the oxidative ring enlargement of furfuryl alcohols, known as Achmatowicz reaction, has been developed to a powerful and versatile synthetic tool for the preparation of 6-hydroxypyranones. This review provides a comprehensive collection of the various ways to perform Achmatowicz rearrangement reactions and explores the role of this ring expansion process in contemporary organic synthesis.
20 Alkylative Amination of Biogenic Furans via Imine-to-Azaallyl Umpolung
F. Blume, M. H. Albeiruty, J. Deska
Synthesis 2015, 47, 2093-2099. Link
Starting from biogenic furfurals, an operationally simple and scalable condensation-umpolung-alkylation protocol was employed in the synthesis of racemic furfurylamines. Subsequent enzymatic kinetic resolution by ω-transaminase or lipase biocatalysts allows for the preparation of functionalized heterocyclic building blocks from biogenic base chemicals in optically pure form.
19 Enzymatic Aerobic Rearrangement of Optically Active Furylcarbinols
D. Thiel, D. Doknic, J. Deska
Nature Commun. 2014, 5, 5278. Link
Biogenic furans are currently discussed as highly attractive alternative feedstock in a post-fossil society; thus, also the creation of sustainable furan valorization pathways appears of great importance. Here an artificial Achmatowicz monooxygenase activity for the aerobic ring expansion of furans is achieved by the combination of commercial glucose oxidase as oxygen-activating biocatalyst and wild-type chloroperoxidase as oxygen-transfer mediator, providing a biological ready-to-use solution for this truly synthetic furan rearrangement. In concert with enzymatic transformations for the enantioselective preparation of optically active furylcarbinols, purely biocatalytic reaction cascades for the stereocontrolled construction of complex pyranones are obtained, exhibiting high functional group tolerance even to oxidation-sensitive moieties.
18 Migratory Dynamic Kinetic Resolution of Carbocyclic Allylic Alcohols
C. Manzuna Sapu, T. Görbe, R. Lihammar, J.-E. Bäckvall, J. Deska*
Org. Lett. 2014, 16, 5952-5955. Link
A novel migratory dynamic kinetic resolution based on the interplay between an enzyme acylation catalyst and a heterogeneous Brønsted acid as an isomerization/racemization catalyst gives rise to carbocyclic allylic esters with excellent stereoselectivity from readily available tertiary carbinols. An easy-to-use teabag setup combining resin-bound catalysts, a biphasic isooctane–water solvent system, and a highly lipophilic acyl donor efficiently suppresses side reactions and allows for the preparation of functionalized carbocyclic building blocks in high yields and optical purity.
17 Young Career Focus
J. Deska, Synform 2014, 1, A14-A15. Link
SYNFORM will from time to time meet young up-and-coming researchers who are performing exceptionally well in the arena of organic chemistry and related fields of research, in order to introduce them to the readership. This SYNSTORY with a Young Career Focus presents Professor Jan Deska, University of Cologne, Cologne, Germany.
16 Oxonium Ylide Rearrangement of Enzymatically Desymmetrized Glutarates
B. Skrobo, J. Deska
Org. Lett. 2013, 15, 5998-6001. Link
The combination of an enzyme-mediated enantioselective desymmetrization of readily available 3-benzyloxy-glutarates and subsequent rhodium-catalyzed oxonium ylide rearrangement of their corresponding in situ derived diazo ketones offers a very concise and highly stereoselective access to functionalized tetrahydro-furanone building blocks.
15 Chemoenzymatic Total Synthesis of Hyperiones A & B
C. Manzuna Sapu, J. Deska
Org. Biomol. Chem. 2013, 11, 1376-1382. Link
The first asymmetric total synthesis of hyperiones A and B, two norlignans from Hypericum chinense, has been accomplished following a chemoenzymatic approach. Key features of this synthesis include the lipase-catalyzed enantioselective desymmetrization of a prochiral allenic diol and a silver-mediated cycloisomerization of the resulting axially chiral product to furnish the furan core structure. Two alternative pathways, a ruthenium-catalyzed redox isomerization on the one side and a platinum-catalyzed hydrogenation on the other, are described to finally obtain the desired norlignans.
14 Modular Synthesis of Optically Active Tröger's Base Analogues
T. Kamiyama, M. S. Özer, E. Otth, J. Deska, J. Cvengros
ChemPlusChem 2013, 78, 1510-1516. Link
For the first time, enantioselective catalysis was applied for the preparation of Tröger's base derivatives affording N-stereogenic building blocks not only in excellent enantiomeric purity but also in an easily scalable fashion. Enzymatic kinetic resolution proved efficient to yield functionalized Tröger's bases, which can be subsequently modified by various chemical methods without any erosion of stereogenic information.
13 On a Chemoenzymatic Desymmetrization/Ring Expansion Strategy towards Functionalized N-Heterocycles
D. Thiel, J. Deska
Synlett 2013, 24, 1529-1532. Link
The direct combination of the desymmetrization of N-hetero-cyclic meso-diols using lipase from Mucor miehei as biocatalyst and subsequent ring expansion of the optically active products by activation of the remaining hydroxy group gives rise to functionalized nonsymmetrical piperidines in a highly enantio- and diastereoselective manner.
12 On the Lipase-catalyzed Resolution of Functionalized Biaryls
B. Skrobo, J. Deska
Tetrahedron: Asymmetry 2013, 24, 1052-1056. Link
The implementation of lipase catalysis as a tool for the preparation of optically active biaryls is discussed. While attempts toward dynamic kinetic resolution based on the catalytic ring opening of configurationally unstable biaryl lactones were fruitless, kinetic resolution via transesterification of hydroxymethyl-decorated substrates was successfully employed in the generation of optically enriched, axially chiral biaryls.
11 Palladium-catalyzed Allylic Alkylation as Versatile Tool in Amino Acid and Peptide Modifications
U. Kazmaier, A. Bayer, J. Deska
Synthesis 2013, 45, 1462-1468. Link
Palladium-catalyzed allylic alkylations are especially suitable for the introduction of γ,δ-unsaturated side chains into amino acids and even peptides. Glycine ester enolates are generally used as nucleophiles in these reactions, they react at a very low temperature (–78 °C) to give the products of isomerization-free allylation. In reactions of cis-configured allylic substrates, the olefin geometry can be transferred to the product. Because the syn position of the corresponding syn/anti π-allyl complex formed in this case is more reactive, this isomerization-free protocol also allows regioselective and stereoselective allylations. Using stannylated allylic substrates gives metalated amino acid derivatives that are ideal substrates for subsequent Stille couplings or tin–iodine exchange reactions. If peptides are deprotonated with excess strong base, the corresponding ester or amide enolates formed can also be subjected to allylation; in this case the stereochemical outcome can be controlled by the peptide chain.
10 Enantioselective Synthesis of Axially Chiral Tetrasubstituted Allenes via Lipase-catalyzed Desymmetrization
M. Hammel, J. Deska
Synthesis 2012, 44, 3789-3796. Link
Lipase from Pseudomonas fluorescens efficiently catalyzes the transesterification of prochiral tetrasubstituted allenic diols yielding highly enantioenriched axially chiral allenyl monoesters. In combination with subsequent 5-endo-trig cyclizations geminally disubstituted dihydrofurans are accessible in high optical purity.
9 Enantioselective Enzymatic Desymmetrization of Prochiral Allenic Diols
C. Manzuna Sapu, J.-E. Bäckvall, J. Deska
Crude lipase from porcine pancreas acts as a highly efficient biocatalyst in the enantioselective transesterification of prochiral allendiols. Following a simple synthetic protocol, highly functionalized axially chiral allenes are obtained in high yields and excellent enantiopurity
8 Stereoselective Synthesis of Deuterated b-Cyclohexenylserine, a Biosynthetic Intermediate of the Salinosporamides
J. Deska, S. Hähn, U. Kazmaier
Org. Lett. 2011, 13, 3210-3213. Link
A straightforward, highly stereoselective protocol toward the synthesis of deuterium-labeled (2R,3S,4S)-β-cyclohexenylserine has been developed. Key steps are a Nozaki–Hiyama–Kishi reaction generating the stereogenic centers and a ring-closing metathesis for the construction of the cyclohexenyl ring system. The labeled amino acid was further activated as an SNAc-ester for feeding experiments.
2006 - 2010