| 1. |
- Jönsson, Christina, et al.
(author)
-
Asymmetric Catalysis in a Micro Reactor : Ce, Yb and Lu Catalysed Enantioselective Addition of Trimethylsilyl Cyanide to Benzaldehyde
- 2004
-
In: Tetrahedron. - : Elsevier BV. - 0040-4020 .- 1464-5416. ; 60:46, s. 10515-10520
-
Journal article (peer-reviewed)abstract
- A T-shaped micro reactor was used for the optimisation of reaction conditions for the enantioselective silyleyanation of benzaldehyde catalysed by lanthanide-pybox complexes. Compared to a conventional batch procedure, higher conversion was observed within shorter reaction time. The micro reactor process involving Lu(III) afforded essentially the same enantioselectivity as the batch process (73 vs 76% ee), whereas the enantioselectivity was lower in the micro reactor for catalysts containing Yb(III) (53 compared to 72%). Ce(III) provided very low selectivity in both types of processes (1 and 11 % ee, respectively). A study of the effect of additives showed that the enantioselectivity in the Yb catalysed reaction performed in the micro reactor could be increased to 66%, whereas only a minor improvement, to 78% ee, was observed in the reaction with Lu.
|
|
| 2. |
- Jönsson, Christina, et al.
(author)
-
Immobilized oxazoline-containing ligands in asymmetric catalysis - A review
- 2002
-
In: Bioorganic & Medicinal Chemistry Letters. - 0960-894X .- 1464-3405. ; 12:14, s. 1857-1861
-
Research review (peer-reviewed)abstract
- Metal complexes of chiral oxazoline derivatives immobilized on soluble as well as insoluble supports serve as versatile asymmetric catalysts in a variety of applications. In a few cases recovery and reuse of the chiral ligands have been achieved.
|
|
| 3. |
- Lundgren, Stina, et al.
(author)
-
Micro reactors for the optimisation of reaction conditions in asymmetric metal catalysis
- 2005
-
In: Micro Total Analysis Systems 2004. - 0854046437 ; , s. 445-447
-
Conference paper (peer-reviewed)abstract
- Two types of micro reactors were employed for enantioselective metal catalysed reactions. In the first type of reactor, an electroosmotic flow was used, whereas the second type of reactor used a pressure driven flow. The purpose of the study is to develop tools for rapid and efficient optimization of reactions, utilising minimum amounts of reagents.
|
|
| 4. |
|
|
| 5. |
|
|
| 6. |
- Andersson, Helene, et al.
(author)
-
Consecutive microcontact printing - ligands for asymmetric catalysis in silicon channels
- 2001
-
In: Sensors and actuators. B, Chemical. - 0925-4005 .- 1873-3077. ; 79:1, s. 78-84
-
Journal article (peer-reviewed)abstract
- Consecutive microcontact printing ( mu CP) has been developed to enable multiple functionalization of silicon surfaces, such as the immobilization of chiral ligands. The technique involves two subsequent printing steps using unstructured poly(methylsiloxane) stamps. The pattern is already defined on the substrate, consisting of etched channels. Hence, no precise alignment is needed between the two printing steps. A carboxylic acid group containing reagent was initially printed onto the silicon oxide surface and transformed to an anhydride. hi the second printing step an ester bond was formed with the hydroxy-functionalized ligand. The formed molecular layers were evaluated by contact angle measurements, scanning electron microscopy (SEM) and electron spectroscopy for chemical analysis (ESCA), indicating that the consecutive mu CP was successful. Initially, printing was performed on planar silicon surfaces but to realize a flow-through microfluidic device for high throughput screening a mu CP technique was developed for etched channels. To verify the technique, hydrophobic valves consisting of octadecyltrichlorosilane were formed using mu CP in deep reactive ion etched channels (50 mum wide and 50 mum deep). The printed hydrophobic patches were visualized by SEM and functioned well. Finally, the consecutive mu CP technique was applied to immobilize the ligand in the channels. The channels were then sealed with a low-temperature bonding technique using an adhesive PDMS film, which does not destroy the printed ligand. In this study mu CP is used in a novel manner. It enables a convenient method for performing complex surface modification of etched structures, which is a frequently appearing problem in biochemical microfluidic systems.
|
|
| 7. |
- Andersson, Helene, et al.
(author)
-
Patterned self-assembled beads in silicon channels
- 2001
-
In: Electrophoresis. - 0173-0835 .- 1522-2683. ; 22:18, s. 3876-3882
-
Journal article (peer-reviewed)abstract
- A novel technique enabling selective bead trapping in microfluidic devices without the use of physical barriers is presented in this paper. It is a fast, convenient and simple method, involving microcontact printing and self-assembly, that can be applied to silicon, quartz or plastic substrates. In the first step, channels are etched in the substrate. The surface chemistry of the internal walls of the channels is then modified by microcontact printing. The chip is submerged in a bead slurry where beads self-assemble based on surface chemistry and immobilize on the internal walls of the channels. Silicon channels (100 mum wide and 50 mum deep) have been covered with monolayers of streptavidin-, amino- and hydroxy-functionalized microspheres and resulted in good surface coverage of beads on the channel walls. A high-resolution pattern of lines of self-assembled streptavidin beads, as narrow as 5 mum, has also been generated on the bottom of a 500 mum wide and 50 mum deep channel. Flow tests were performed in sealed channels with the different immobilized beads to confirm that the immobilized beads could withstand the forces generated by water flowing in the channels. The presented results indicate that single beads can be precisely positioned within microfluidic devices based on self-assembly which is useful as screening and analysis tools within the field of biochemistry and organic chemistry.
|
|
| 8. |
- Andersson, Helene, et al.
(author)
-
Self-assembled and self-sorted array of chemically active beads for analytical and biochemical screening
- 2002
-
In: Talanta. - 0039-9140 .- 1873-3573. ; 56:2, s. 301-308
-
Journal article (peer-reviewed)abstract
- A technique for generating a general screening platform consisting of dots of immobilized beads on silicon has been developed via self-sorting and -assembly of different kinds of beads. The dots are defined by a teflon-like film, which due to its hydrophobic characteristics also prevents cross-contamination of liquid from different dots. To enable functionalization of individual dots with different target molecules simultaneously a new way of microcontact printing has been explored where different target solutions are printed in parallel using one stamp. In order to show that this platform can be designed for both biochemical assays and organic chemistry, streptavidin-, amino- and hydroxy-functionalized beads have been self-sorted and -assembled both on separate and common platforms. The self-sorting and -arrangement are based on surface chemistry only, which has not previously been reported. Beads of different sizes and material have successfully been immobilized in line patterns as narrow as 5 mum. Besides silicon, quartz and polyethylene have also been used as substrates.
|
|
| 9. |
- Belda, O., et al.
(author)
-
Bispyridylamides - coordination chemistry and applications in catalytic reactions
- 2005
-
In: Coordination chemistry reviews. - : Elsevier BV. - 0010-8545 .- 1873-3840. ; 249:06-maj, s. 727-740
-
Research review (peer-reviewed)abstract
- Complexes of bis(2-pyridylamides) with most metal ions have been described. A variety of coordination modes, with the neutral or the deprotonated amide functions binding either via the carbonyl oxygen atom or the amide nitrogen atom have been identified. The modular technique used for the preparation of the compounds permits facile access to ligands with substituted pyridine nuclei and ligands with different backbones. Moreover, symmetric as well as asymmetric compounds, with equal or different pyridine rings and with symmetric or non-symmetric amines, can conveniently be prepared. Chiral derivatives are easily obtained starting from chiral diamines. Several metal complexes have been studied as mimics of biological systems. In recent years a variety of metal complexes have also been employed in catalysis. Oxidations of alkanes and alkenes have been particularly well studied, although modest reactivity has usually been encountered. Other applications include their use as ligands in Lewis acid catalyzed processes. Recently, it was shown that complexes with molybdenum catalyze highly regio- and enantioselective allylic alkylations.
|
|
| 10. |
- Belda, Oscar, et al.
(author)
-
Chiral bispyridylamide metal complexes as catalysts for the enantioselective adddition of TMSCN to aldehydes
- 2004
-
In: Journal of Organometallic Chemistry. - : Elsevier BV. - 0022-328X .- 1872-8561. ; 689:23, s. 3750-3755
-
Journal article (peer-reviewed)abstract
- The use of (1R,2R)-N,N'-bis(2-pyridinecarboxyamido)-1,2-diphenylethane metal complexes as catalysts for the enantioselective addition of trimethylsilyl cyanide to aldehydes is described. Enantioselectivities up to 70% ee were obtained with a Ti(IV) catalyst. Complexes with Zr(IV), Sc(III), Yb(III) and Cu(II) afforded less selective catalysts. For the Zr(IV) complex, a rate and selectivity enhancement was observed when adding 0.5 equiv. of water with respect to the catalyst. Studies of the metal complexes involved in the reaction were carried out by means of H-1 NMR spectroscopy. A Zr complex was shown by X-ray crystallography to exhibit distorted octahedral coordination, with the four nitrogen atoms of the doubly deprotonated ligand essentially in one plane.
|
|
| 11. |
- Belda, O., et al.
(author)
-
Highly stereo- and regioselective allylations catalyzed by Mo-pyridylamide complexes : Electronic and steric effects of the ligand
- 2000
-
In: Journal of Organic Chemistry. - Uppsala Univ, Uppsala Biomed Ctr, Dept Organ Pharmaceut Chem, SE-75123 Uppsala, Sweden. Royal Inst Technol, Dept Chem, SE-10044 Stockholm, Sweden. : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 65:18, s. 5868-5870
-
Journal article (peer-reviewed)
|
|
| 12. |
- Belda, Oscar, et al.
(author)
-
Molybdenum-catalyzed asymmetric allylic alkylations
- 2004
-
In: Accounts of Chemical Research. - : American Chemical Society (ACS). - 0001-4842 .- 1520-4898. ; 37:3, s. 159-167
-
Journal article (peer-reviewed)abstract
- The highly regio- and enantioselective molybdenum-catalyzed allylic alkylation reaction has become a powerful synthetic tool during the past few years. This Account describes the achievements gained so far in the area, with special attention directed to the different chiral ligands that have been used for inducing chirality in the products, the range of allylic substrates and nucleophiles employed, mechanistic studies, and applications of the reaction in asymmetric syntheses.
|
|
| 13. |
- Belda, O., et al.
(author)
-
Recoverable resin-supported pyridylamide ligand for microwave-accelerated molybdenum-catalyzed asymmetric allylic alkylations : Synthesis of baclofen
- 2003
-
In: Organic Letters. - : American Chemical Society (ACS). - 1523-7060 .- 1523-7052. ; 5:13, s. 2275-2278
-
Journal article (peer-reviewed)abstract
- The syntheses of a series of 4-monosubstituted pyridylamides and a resin-supported pyridylamide are described. The ligands were evaluated in the microwave-accelerated molybdenum-catalyzed asymmetric allylic alkylation. The reaction afforded the product in high yield and with high regio- and enantioselectivity. The heterogeneous ligand could be reused several times with no change in the reaction outcome. The asymmetric allylic alkylation was employed as the key step in the enantioselective synthesis of (R)-baclofen.
|
|
| 14. |
- Belda, O., et al.
(author)
-
Substituted pyridylamide ligands in microwave-accelerated Mo(0)-catalysed allylic alkylations
- 2002
-
In: Synthesis (Stuttgart). - 0039-7881 .- 1437-210X. ; :11, s. 1601-1606
-
Journal article (peer-reviewed)abstract
- Novel 4- and 6-substituted bis-pyridylamides were prepared by microwave accelerated nucleophilic substitution of the 4-and 6-halo substituted derivatives of the parent ligand la. The ligands were used in the asymmetric allylation of cinnamyl carbonate catalysed by Mo(0) in which the 4-chloro- and 4-pyrrolidyl substituted ligand derivatives exhibited high regioselectivity (74:1 and 88:1. respectively) and enantioselectivity (96% ee), whereas 6-substituted ligands afforded no product under the same conditions. Other allylic substrates were used to explore the generality of the procedure.
|
|
| 15. |
|
|
| 16. |
- Bellini, Rosalba, et al.
(author)
-
Conformational Preferences of a Tropos Biphenyl Phosphinooxazoline-a Ligand with Wide Substrate Scope
- 2016
-
In: Acs Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 6:3, s. 1701-1712
-
Journal article (peer-reviewed)abstract
- Excellent enantioselectivities are observed in palladium-catalyzed allylic substitutions of a wide range of substrate types and nucleophiles using a bidentate ligand composed of oxazoline and chirally flexible biaryl phosphite elements. This unusually wide substrate scope is shown by experimental and theoretical studies of its eta(3)-allyl and eta(2)-olefin complexes not to be a result of configurational interconversion of the biaryl unit, since the ligand in all reactions adopts an S-a,S configuration on coordination to palladium, but rather the ability of the ligand to adapt the size of the substrate-binding pocket to the reacting substrate. This ability also serves as an explanation to its excellent performance in other types of catalytic processes.
|
|
| 17. |
- Berg, Marie, 1955, et al.
(author)
-
Room4Birth - the effect of an adaptable birthing room on labour and birth outcomes for nulliparous women at term with spontaneous labour start: study protocol for a randomised controlled superiority trial in Sweden
- 2019
-
In: Trials. - : Springer Science and Business Media LLC. - 1745-6215 .- 1745-6215. ; 20:1
-
Journal article (peer-reviewed)abstract
- BACKGROUND: An important prerequisite for optimal healthcare is a secure, safe and comfortable environment. There is little research on how the physical design of birthing rooms affects labour, birth, childbirth experiences and birthing costs. This protocol outlines the design of a randomised controlled superiority trial (RCT) measuring and comparing effects and experiences of two types of birthing rooms, conducted in one labour ward in Sweden. METHODS/DESIGN: Following ethics approval, a study design was developed and tested for feasibility in a pilot study, which led to some important improvements for conducting the study. The main RCT started January 2019 and includes nulliparous women presenting to the labour ward in active, spontaneous labour and who understand either Swedish, Arabic, Somali or English. Those who consent are randomised on a 1:1 ratio to receive care either in a regular room (control group) or in a newly built birthing room designed with a person-centred approach and physical aspects (such as light, silencer, media installation offering programmed nature scenes with sound, bathtub, birth support tools) that are changeable according to a woman's wishes (intervention group). The primary efficacy endpoint is a composite score of four outcomes: no use of oxytocin for augmentation of labour; spontaneous vaginal births (i.e. no vaginal instrumental birth or caesarean section); normal postpartum blood loss (i.e. bleeding < 1000 ml); and a positive overall childbirth experience (7-10 on a scale of 1-10). To detect a difference in the composite score of 8% between the groups we need 1274 study participants (power of 80% with significance level 0.05). Secondary outcomes include: the four variables in the primary outcome; other physical outcomes of labour and birth; women's self-reported experiences (the birthing room, childbirth, fear of childbirth, health-related quality of life); and measurement of costs in relation to the hospital stay for mother and neonate. Additionally, an ethnographic study with participant observations will be conducted in both types of birthing rooms. DISCUSSION: The findings aim to guide the design of birthing rooms that contribute to optimal quality of hospital-based maternity care. TRIAL REGISTRATION: ClinicalTrials.gov NCT03948815. Registered 13 May 2019-retrospectively registered.
|
|
| 18. |
- Bergström, Eva-Karin, 1974, et al.
(author)
-
Approximal caries increment in adolescents in a low caries prevalence area in Sweden after a 3.5-year school-based fluoride varnish programme with Bifluorid 12 and Duraphat
- 2014
-
In: Community Dentistry and Oral Epidemiology. - : Wiley. - 0301-5661. ; 42:5, s. 404-411
-
Journal article (peer-reviewed)abstract
- ObjectivesTo evaluate approximal caries increment among 12- to 16-year-olds in a low caries prevalence area in Sweden after a 3.5-year school-based fluoride (F) varnish programme with Bifluorid 12 and Duraphat. MethodsThe design was a RCT study with 1365 adolescents, divided into following four groups: Group 1 Bifluorid 12 two applications/year; Group 2 Duraphat two applications/year; Group 3 Bifluorid 12 four applications/year and Group 4 no F varnish at school. 1143 children (84%) completed the study. Approximal caries was registered on bitewing radiographs. ResultsThere were no statistically significant differences in caries prevalence among the groups either at baseline or after 3.5years . The caries increment for Group 1 was 1.342.99 (mean +/- SD), 1.24 +/- 2.84 for Group 2, 1.07 +/- 2.66 for Group 3 and 1.25 +/- 2.75 for Group 4, with no statically significant differences either between Bifluorid 12 and Duraphat with the same frequency of F varnish applications or between the F groups and the control group. ConclusionsIn an area with low caries prevalence in Sweden, the supplementary caries-preventive effect of school-based F varnish applications, to regular use of F toothpaste at home and to regular caries prevention given at the Public Dental Clinics, appears to be nonsignificant regarding approximal caries increment.
|
|
| 19. |
- Bourguignon, J., et al.
(author)
-
Chiral ditopic receptors. Application to palladium-catalyzed allylic alkylation
- 2003
-
In: Tetrahedron. - : Elsevier BV. - 0040-4020 .- 1464-5416. ; 59:48, s. 9583-9589
-
Journal article (peer-reviewed)abstract
- Chiral pyridinooxazoline, quinolinooxazoline, bis(oxazolino)pyridine (pybox), and bisoxazoline (box) derivatives containing crown ether residues were prepared. Some of the ligands were assessed in substrate binding studies and in palladium catalyzed allylic alkylations.
|
|
| 20. |
- Brule, Emile, et al.
(author)
-
Chelating phosphines with C-2 and C-3 symmetry
- 2004
-
In: Mendeleev communications (Print). - 0959-9436 .- 1364-551X. ; :6, s. 276-277
-
Journal article (peer-reviewed)abstract
- Antide formation between ring opened aziridines and 2-(diphenylphosphino)benzoic acid provides an easy access to chelating di- and triphosphines with C-2 and C-3 symmetry.
|
|
| 21. |
- Del Litto, Raffaella, et al.
(author)
-
Carbohydrate-Based Pyridine-2-carboxamides for Mo-Catalyzed Asymmetric Allylic Alkylations
- 2009
-
In: European Journal of Organic Chemistry. - : Wiley. - 1434-193X .- 1099-0690. ; :9, s. 1352-1356
-
Journal article (peer-reviewed)abstract
- Bis(pyridine-2-carboxamides) were prepared from 1,2-diamines obtained from alpha-D-ghlcose and alpha-D-mannose. The ligands were assessed in molybdenum-catalyzed asymmetric allylic alkylations (AAA) by using both methyl (E)-3-phenyl-2-propenyl and methyl rac-1-phenyl-2-propenyl carbonates and dimethyl malonate as nucleophile under microwave irradiation. High enantioselectivity (99 % ee) and high regioselectivity (49:1 in favour of the branched isomer) were observed in reactions of the linear achiral substrate in the presence of 10 mol-% of a catalyst prepared from a ligand derived from glucose. Somewhat lower enantioselectivity (up to 96 % ee) was observed in reactions with the branched racemic carbonate by using the same ligand. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
|
|
| 22. |
- Dieguez, Montserrat, et al.
(author)
-
Self-Adaptable Tropos Catalysts
- 2021
-
In: Accounts of Chemical Research. - : American Chemical Society (ACS). - 0001-4842 .- 1520-4898. ; 54:16, s. 3252-3263
-
Research review (peer-reviewed)abstract
- Biological systems have often served as inspiration for the design of synthetic catalysts. The lock and key analogy put forward by Emil Fischer in 1894 to explain the high substrate specificity of enzymes has been used as a general guiding principle aimed at enhancing the selectivity of chemical processes by optimizing attractive and repulsive interactions in molecular recognition events. However, although a perfect fit of a substrate to a catalytic site may enhance the selectivity of a specific catalytic reaction, it inevitably leads to a narrow substrate scope, exduding substrates with different sizes and shapes from efficient binding. An ideal catalyst should instead be able to accommodate a wide range of substrates-it has indeed been recognized that enzymes also are often highly promiscuous as a result of their ability to change their conformation and shape in response to a substrate-and preferentially be useful in various types of processes. In biological adaptation, the process by which species become fitted to new environments is crucial for their ability to cope with changing environmental conditions. With this in mind, we have been exploring catalytic systems that can adapt their size and shape to the environment with the goal of developing synthetic catalysts with wide scope. In this Account, we describe our studies aimed at elucidating how metal catalysts with flexible structural units adapt their binding pockets to the reacting substrate. Throughout our studies, ligands equipped with tropos biaryl units have been explored, and the palladium-catalyzed allylic alkylation reaction has been used as a suitable probe to study the adaptability of the catalytic systems. The conformations of catalytically active metal complexes under different conditions have been studied by both experimental and theoretical methods. By the design of ligands incorporating two flexible units, the symmetry properties of metal complexes could be used to facilitate conformational analysis and thereby provide valuable insight into the structures of complexes involved in the catalytic cycle. The importance of flexibility was convincingly demonstrated when a phosphine group in a privileged ligand that is well-known for its versatility in a number of processes was exchanged for a tropos biaryl phosphite unit: the result was a truly self-adaptive ligand with dramatically increased scope.
|
|
| 23. |
- Durieux, Guillaume, et al.
(author)
-
Rate and Mechanism of the Oxidative Addition of a Silylborane to Pt0 Complexes : Mechanism for the Pt-Catalyzed Silaboration of 1,3-Cyclohexadiene
- 2008
-
In: European Journal of Inorganic Chemistry. - Weinheim : Wiley-VCH. - 1434-1948 .- 1099-1948 .- 1099-0682. ; :27, s. 4236-4241
-
Journal article (peer-reviewed)abstract
- The chemical reduction of Pt(acac)(2) by DIBALH in the presence of phosphanes, which is used to generate active Pt-0 complexes in the Pt-catalyzed silaboration of cyclohexadiene by 2-(diinethylphenylsilyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (1) leading to the 1,4-silaborated product, was mimicked by the electrochemical reduction of Pt(acac)(2) in the presence of 2 equiv. of PR3 (R = Ph, nBu). The electrochemical reduction generates free acac anions and neutral Pt-0-(PR3)(2) complexes. The kinetics of the oxidative addition of bromobenzene (used first as a model molecule) and silylborane 1 to the Pt-0 complexes was investigated and the rate constants determined. Pt-0(PnBu(3))(2) is much more reactive than Pt-0(PPh3)(2) towards 1. From the electrochemical study, it emerges that the acac anions released in the reduction of Pt(acac)(2) do not coordinate to the Pt-0(PR3)(2) complexes. Consequently, the rate of the oxidative addition of 1 to Pt-0(PR3)(2), generated either by the electrochemical reduction or by the chemical reduction by DIBALH, is not affected by the acac anions and a posteriori not by aluminum cations. The oxidative addition and the further step of the catalytic cycle [insertion of the diene into the Pt-B bond of the Si-Pt-B complex generated in the oxidative addition, with formation of the eta(3)-allyl)Pt-Si complex] were monitored by NMR spectroscopy. Pt-0 and Pt-II complexes involved in the catalytic cycle were characterized. The oxidative addition is faster when the ligand is PMe2Ph relative to that obtained with PPh3, in agreement with the electrochemical data. No reductive elimination within the ((eta(3)-allyl))Pt-Si complex is observed when the ligand is PMe2Ph, whereas reactions in the presence of PPh3 proceeded to give the final product. As a consequence, PPh3 is a better ligand than PMe2Ph for the catalytic reaction, as observed experimentally.
|
|
| 24. |
- Engqvist, Magnus, 1973-
(author)
-
Direct Amino Acid-Catalyzed Enantioselective α-Oxidation Reactions and Asymmetric de novo Synthesis of Carbohydrates
- 2005
-
Doctoral thesis (other academic/artistic)abstract
- The ability of amino acids to form nucleophilic enamines with aldehydes and ketones has been used in the development of asymmetric α-oxidation reactions with electrophilic oxidizing agents. Singlet molecular oxygen has for the first time been asymmetrically incorporated into aldehydes and ketones, and the products were isolated as their corresponding diols in good yields and ee’s. Organocatalytic α-oxidations of cyclic ketones with iodosobenzene and N-sulfonyloxaziridine were also possible and furnished after reduction the product diols in generally low yields and in low to good ee’s. Amino acids have also been shown to catalyze the formation of carbohydrates by sequential aldol reactions. For example, proline and hydroxy proline mediate a highly selective trimerisation of α-benzyloxyacetaldehyde into allose, which was obtained in >99 % ee. Non linear effect studies of this reaction revealed the largest permanent nonlinear effect observed in a proline-catalyzed reaction to date. Moreover, polyketides were also assembled in a similar fashion by an amino acid-catalyzed one-pot reaction, and was successful for the trimerisation of propionaldehyde, however the sequential cross aldol reactions suffered from lower selectivities. This problem was overcome by the development of a two-step synthesis that enabled the formation of a range of polyketides with excellent selectivities from a variety of aldehydes. The method furnishes the polyketides via the shortest route reported and in comparable product yields to most multi-step synthesis. All polyketides were isolated as single diastereomers with >99 % ee. Based on the observed amino acid-catalysis, amino acids are thought to have taken part in the prebiotic formation of tetroses and hexoses.
|
|
| 25. |
- Eriksson, Carina, 1973-
(author)
-
Isolation, Synthesis and Structure-Activity Relationships of Antifeedants against the Pine Weevil, Hylobius Abietis
- 2006
-
Doctoral thesis (other academic/artistic)abstract
- The large pine weevil, Hylobius abietis L., is a major insect pest on conifer seedlings in northern Europe. Due to its feeding newly planted trees get girdled, resulting in high seedling mortality (up to 80%). As a consequence great financial losses to the forest industry occur. Today the seedlings are protected with the pyrethroid insecticide cypermethrin. This insecticide is toxic to aquatic organisms and is, from 2010, prohibited for use in Sweden by the Swedish Chemicals Inspectorate. An alternative to insecticides is to protect the seedlings with antifeedants, compounds that, either through taste or smell or both, deter the weevils from feeding. This thesis describes the search for and the synthesis of such antifeedant compounds. Bark extracts of several woody species, known to be non-palatable to the weevil, were prepared and found to display antifeedant activity against H. abietis. The major chemical constituents of the extracts were tested for antifeedant activity. Antifeedants such as eugenol, 2-phenylethanol and benzylalcohol, but also feeding stimulants such as β-sitosterol and linoleic acid, were identified. An extract of linden bark, Tilia cordata, was shown to contain nonanoic acid, a highly active antifeedant. Other aliphatic carboxylic acids were also found to display high antifeedant activities against the weevil, both in laboratory and in field tests. The enantiomers of dihydropinidine, a piperidine alkaloid present in several conifer species, were prepared by dimethylzinc mediated allylation of 2- methyltetrahydropyridine-N-oxide. When tested in micro feeding assays, no difference in antifeedant activity was found for the enantiomers. In a field test high antifeedant activity, comparable with that of the presently used insecticide cypermethrin, was found for (±)-dihydropindine. Other naturally occurring piperidine alkaloids were synthesised and also found to display high antifeedant activities in laboratory tests. Structure-activity relationships were evaluated for methoxy substituted benzaldehydes, benzoic acids and cinnamic aldehydes, -acids, -esters and -alcohols. While the carboxylic acids were inactive or even feeding stimulants, the aldehydes were the most active antifeedants
|
|
