according toIUPACThe definition of the Golden Book, asymmetric synthesis, also known as chiral synthesis, stereoselective synthesis, and enantioselective synthesis, is to study the introduction of one or morechiralityOf an elementchemical reactionOfOrganic synthesisBranch.According to Morrison and Mosher's definition, asymmetric composition is "aOrganic reaction, wheresubstrateNon in molecular wholechiralityThe unit is converted into chiral unit by the way of producing stereoisomeric products in unequal amounts from the reactant ".Here, the reagent can beChemical Reagents、catalyzer、solventOr physical factors.
It is also called asymmetric synthesis, which generates optically active products.In the reaction process, due to the influence of intra molecular or extra molecular chirality factors, the reagent attacks both sides of a symmetric structure of the reactant, and then shows uneven chemical bond formation, resulting in unequal amounts of mixtures of stereoisomers with optical activity.[1]
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Asymmetric synthesis is currentlymedicineSynthetic and natural productstotal synthesisBoth have a very important position.But there is no doubt that the most perfect asymmetric synthesis technology now is the enzyme existing in the organism.It is a challenge to human intelligence to realize a catalytic system as efficient as enzyme.
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Generally speaking, an asymmetric synthesis can be regarded as a success criterion:
reagentControl: the reaction of non chiral substrates with chiral reagents - chiral auxiliaries, asymmetric catalysis;
Bisymmetric reaction: the enantiomeric pure substrate reacts with the enantiomeric pure reagent.
SometimesChiral resolutionAlso counted as a type of asymmetric synthesis.
In addition, forchiralitySome people divide asymmetric synthesis into ordinary asymmetric synthesis and absolute asymmetric synthesis.
General asymmetric synthesis refers to the process that is directly or indirectly obtained from natureChiral compoundDerivative groups induce the synthesis of chiral compounds.Absolute asymmetric synthesis means absolute separationnatural productSource by physical method (e.g. by circlePolarizationInduced productionchiralitySynthesis of.The latter takes a lot of effort, so currently only a very limited number of reactions can achieve absolute asymmetric synthesis.
stayOrganic compoundMedium, compoundmoleculeThe skeleton is mainly composed of carbon carbon bonds connected with each other.When the carbon atoms are bonded, the sp3 hybrid method is adopted, so that the four valence bonds of the carbon atoms are 109 degrees 28 minutes each other, which is oneRegular tetrahedronShape.Because of this bondingcharacteristic, resulting in some carbon atoms among them. Although the four groups they combine are of the same type, they can never coincide. The two are mirror images of each other, just like our left hand and right hand.This property is calledchirality。We call two mirror imagesmoleculebyEnantiomer。
Secondly, what is asymmetric synthesis?
In order to obtain one chirality of the same substancemoleculeWe need to adopt a specific synthesis method, which is called asymmetric synthesis.
Then, we will discuss that the asymmetric synthesis product with a certainchiralityOfmoleculeWhat kind do you havecharacteristic？
Chiral moleculeThe biggest feature is its optical activity, which can makepolarized lightWhen a certain angle of deflection occurs, we usuallysignificanceOnoptical rotation。If the direction of light rotation isClockwise, called dextral rotation;Conversely, it is called left-hand rotation.
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What does asymmetric synthesis look likesignificance？
Let's give some simple examples.Penicillin is very familiar to us. It is a powerful antibiotic with little side effectsmedicine, has been widely used for a long time.However, recently it was found that penicillinmoleculeThere are also twoChiral moleculeOne of them is effective, while the other is not.In other words, we spent a bottle of penicillin, but only half of it was useful, which was a great waste.Of course, waste is acceptable, but there aremedicinetwo typesChiral moleculeOne of them not only has no efficacy, but also has quite strong side effects.In the middle of last century, pregnant women often used a drug called thalidomide to inhibitPregnancy reaction, but produced a large number of deformed fetuses.It was later discovered thatmedicinetwo typesChiral moleculeOne of them has the effect of deforming fetus.
not onlymedicineSome food additives also have such problems.Of the two chiral molecules, one is sweet and the other is bitter.
So it can be seen that we are interested inResearchYes, very muchsignificanceIt is also very necessary.
Technical development stage
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(1) asymmetric reaction of chiral source;
(2) asymmetric reaction of chiral auxiliaries;
(3) asymmetric reaction of chiral reagents;
(4) Asymmetric catalytic reaction.
In traditional asymmetric synthesis, asymmetric factors are introduced into symmetric initial reactants or reacted with asymmetric reagents, which requires the use of stoichiometric chiral auxiliary reagents.Asymmetric catalytic synthesis generally refers to the use of a reasonably designed chiral metal complex (amount of catalyst) or biological enzyme as a chiral template to control the enantiomeric surface of the reactant, and selectively convert a large number of prochiral substrates into products of a specific configuration to achieve chiral amplification and chiral proliferation.In short, it is to produce a large number of products with chiral characteristics stereoselectively by using chiral raw materials of catalyst level.Its reaction conditions are mild, stereoselectivity is good, (R) - isomers or (S) - isomers are also easy to produce, and the source of prochiral substrates is wide, which is the most economical and practical technology for the production of a large number of chiral compounds.Therefore, asymmetric catalytic reactions (including chemical catalysis and biocatalytic reactions) have been highly valued by organic chemists all over the world, especially many chemical companies are committed to developing asymmetric catalytic reactions into chiral science and asymmetric synthesis processes.
