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Chemical synthesis of antifeedant – natural products from the coca cola tree

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Chemical synthesis of antifeedant – natural products from the coca cola tree
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We describe an enantioselective synthetic route to the leucosceptroid family of natural products that allowed to synthesize several members of this natural product familiy. The cotton bollworm (Helicoverpa armigera) and the beet armyworm (Spodoptera exigua) are among the most destructive agricultural pests in nature and they affect vegetables and other crops worldwide. Protection against them has been achieved by the use of sex-pheromone traps, insecticides, and transgenic crops. However, resistance to insecticides has developed over the last decade and new chemical agents are necessary to prevent further crop damage from these pests. Leucosceptrum canum Smith (“Bird’s Coca Cola tree”) and Colquhounia coccinea var. mollisa, plants found in China and Nepal, are remarkably resistant to herbivores and pathogens. Extraction and isolation of the trichomes, flowers, and whole leaves recently led to the discovery of novel antifeedant „leucosceptroid“ natural products. So far, no general and practical strategy which allows for the collective synthesis of the leucosceptroid family of natural products was available to the scientific community. Herein, we describe an enantioselective synthetic route to the leucosceptorids that allowed to synthesize several members of this natural product familiy. Additionally, we were able to partially mimic the biosynthetic pathway and the current findings support the hypothesis that two biosynthetic pathways are operative in the plant. The presented results should also serve as an example that, today, total synthesis is capable of providing practical access to a whole natural product family and deliver ample quantities of important intermediates as wells as the target compounds for further biological investigations.
Keywords
ChemistryChemical synthesisCoca-ColaFunctional groupChemistrySynthetic oilOrganic chemistryTotalsyntheseMeeting/Interview
SchwermetallOrganic chemistryChemical plantPhenobarbitalMoleculeChemistryChemical compoundMeeting/Interview
PharmaceuticsAntibacterialChemotherapyMeeting/Interview
NaturstoffChemical plantMeat analogueChemical compoundThermoformingTotalsyntheseMeeting/Interview
Chemical reactionChemical compoundMeat analogueOcean currentSmoking (cooking)SymptomMeeting/Interview
Ocean currentMoleculeTotalsyntheseMeeting/Interview
MoleculeChemische SyntheseTotalsyntheseNaturstoffChemical structureActivity (UML)Chemical experiment
Activity (UML)NaturstoffChemical structureMolecule
Chemical structureButcherMoleculeBlock (periodic table)Multiprotein complexAlcoholSynthetic oil
MoleculeChiralität <Chemie>Materials scienceAlcoholMultiprotein complexProcess (computing)
Multiprotein complexMoleculeLecture/Conference
WalkingTotalsyntheseProcess (computing)Klinisches ExperimentMaterials scienceMolecule
Materials scienceMolecule
NaturstoffChemical compoundSynthetic oilComputer animationMeeting/Interview
Nuclear magnetic resonanceComputer animationDiagram
ProteinNaturstoffSynthetic oilComputer animation
Nuclear magnetic resonanceMan pagePainFunctional groupChain (unit)Computer animation
Functional groupSide chainAcetylMolecular geometryComputer animation
MoleculeHydrophobic effectNaturstoffChemical structureActive siteChemical compoundMolecular geometryComputer animationMeeting/Interview
Side chainChemical structureHydrophobic effectChemical experimentMeeting/Interview
Chemical compoundData conversionComputer animation
MethanolOxideData conversionSolutionComputer animation
MethanolChemical reactionQuartzChemical experiment
CobaltoxideSolutionChemical reactionChemical experiment
PeroxideElectronic cigaretteChemical experiment
CycloadditionFunctional groupChemical experiment
MethanolPeroxideHydroperoxideFunctional groupChemical reactionDimethylsulfidMoleculeSulfideMetalWalkingElectronic cigaretteHydro TasmaniaMolecular geometryComputer animation
Aldol reactionChemical reactionReducing agentHydroperoxideTriethylaminOxideChemical experiment
Chemical reactionAldol reactionSample (material)MixtureChemical experiment
Chemical reactionSilicon dioxideHyperpolarisierungWater purificationChemical compoundColumn chromatographyConcretionSea levelMolecular geometryChemical experimentMeeting/Interview
Separator (milk)Setzen <Verfahrenstechnik>ThermoformingChromatographySample (material)Electronic cigaretteNanoparticleSystemic therapyBreed standardChemical compoundSilicon dioxideHigh-performance liquid chromatographyOvenZigarettenschachtel
Sample (material)Phase (waves)ChromatographyChemical reactionChemical experimentMeeting/Interview
Separator (milk)TotalsyntheseFunctional groupAreaMoleculeHope, ArkansasWursthülleChemical structureComputer animationMeeting/Interview
Transcript: English(auto-generated)
Welcome everyone. My name is Thomas Margauer and I'm an assistant professor at the Department of Chemistry at LMU Munich.
My research group is working on the development of new synthetic methods and its application for organic synthesis. Today we are at the Botanical Garden here in Munich surrounded by more than 15,000 plants. So one might ask himself, why or how is organic chemistry connected to plants? Well, plants produce molecules which can be used by them as a signaling agent or also as a protection against heavy wars.
On the other hand, humans can also harvest these compounds and use them as pharmaceuticals such as antibiotics or anti-cancer agents. Since the production of natural compounds by plants is often limited, organic synthesis allows for an alternative access to these compounds.
Not only can we make these compounds in their natural form, but we also are able to synthesize analogs which have a unique reaction profile and unique bio-profile. In one of our current research projects, we work on the synthesis of antifedent molecules from leucoseptum kanamismus.
My co-workers are now going to show you which equipment and which techniques are necessary to realize such a project. Hi, I'm Cedric. I'm a PhD student in the laboratory of Thomas Malgauer and I'm currently working on the total synthesis of natural products. The very basic concept of a total synthesis is to develop a synthetic route to a target molecule.
We chose nor-leucoseptide A, the structure shown here, as our target molecule. This natural product was isolated from a tree growing in the southwest of China and it has shown to exhibit antifedent activity against, for example, the cotton bollworm and the beet armyworm.
The biological activity, as well as the challenging structure of nor-leucoseptide A, therefore make this a very attractive synthetic target. So in our retro-synthetic analysis of nor-leucoseptide A, we imagined to first cut these two bonds. This would lead us back to this tricyclic structure and here again we will cut these bonds, leading us to this simplified tricyclic structure.
We imagined constructing this intermediate from two similarly complex building blocks by more
or less cutting the molecule in half and obtaining these two building blocks. In turn, these we will be able to construct from commercially available building blocks. This one from the homoallylic alcohol shown here and the right hand part of the molecule from a commercially available chiral pool building block, which is R-Pulagon.
Once we've established this retro-synthetic plan, we start conducting experiments with these two commercially available starting materials
and stepwise increase the complexity of our products, reaching these intermediates and finally arriving at our target molecule. This process involves many experiments and also a considerable amount of trial and error. Fortunately, we were able to complete the total synthesis of nor-leucoseptide A in 16 steps from the commercially available starting
materials and my colleague will now show you how we can be actually sure that we have made the desired target molecule. My name is Adriana Grossmann and I will now explain to you two analytical methods with which we can explain that the isolated natural product and our synthesized natural product are really the same compounds.
The first experiment we did was a 1H NMR spectra. Here I show you the protein NMR spectra of the synthetic natural product and of the isolated natural product. As we can see, the signals of the synthetic natural product fit completely to the one of the isolated natural product.
But we did not only do NMR experiments but also got crystal structures. One I can show you here. Here we can see the isopropanol group from the side chain and this is the elementin skeleton with the acetyl group.
By these two analytical methods, we were able to prove that the synthesized molecule is identical with the isolated one. Nor-leucoseptide A actually is only one of about 30 members of related natural products. Two further ones are shown here and are leucoseptide A and leucoseptide C which both contain a similar core structure but a different side chain.
Most recently, we became interested in the biogenetic relationship between these compounds and we believe that an oxidative degradation of leucoseptide A gives rise to leucoseptide C. And we would like to mimic this biomimetic conversion in a flask.
I've prepared a solution of leucoseptide A in methanol and I will add just a few crystals of rose Bengal which will act as a photosensitizer in the following reaction.
I will now start bubbling oxygen gas through the solution and cool the solution to minus 78 degrees. Thereupon, to actually start the reaction, I irradiate this solution with light. A formal 4 plus 2 cycloaddition with the furan moiety takes place.
This gives an intermediate as shown here. I'm only drawing the furan moiety here which is an endo peroxide. Since the reaction is conducted in methanol as a solvent, next one molecule
of methanol will add nucleophilically to this endo peroxide giving rise to this hydroperoxide.
In the next step, we will discontinue the irradiation and add dimethyl sulfide to reduce the peroxide and then let the solution warm up to room temperature. Now that the reaction mixture has reached room temperature and the reduction of
the hydroperoxide is complete, I will add triethylamine to induce the aldol reaction. After the addition of triethylamine, we let the reaction mixture stir for a few hours until the aldol reaction is complete. Unfortunately, this aldol reaction is not perfectly selective and we obtain a mixture of diastereomers at these two positions.
My co-worker will now show you how we can separate the diastereomers and obtain analytically pure samples of both diastereomers. My name is Klaus, I'm a PhD student in the Margot Laboratories and I will now show you how to further purify satyr compounds.
Like briefly mentioned in the reaction satyr conducted, two diastereomers are formed which are normally hard to separate via column chromatography and silica gel. As they are very much alike and the polarity is almost the same, we need an HPLC. Here you can see a standard high performance liquid chromatography setup.
The two pumps, the column which is placed in the column oven and the main advantage of these columns is that in general the particles are smaller and more tightly packed and this tight packing allows for better separation on a normal silica gel chromatography column. After the compounds pass through the column, they are detected by the UV detector which then get collected in our automated fraction collecting system.
I will now inject our pre-purified sample on a reverse phase column. So after the run is finished, we can see on this chromatogram two individual peaks. Each peak corresponds to one diastereomer as predicted by the reaction outcome.
This nice separation could be achieved using an HPLC. I hope we could show you that organic synthesis is an exciting and rewarding research area. Not only can you design your own structures, but also can you make molecules. We are currently investigating molecules from Leukocypton Smith together with a research group from China for safe crop protection.