Transcript for:
Amino acids, peptides, and proteins

good morning morning well so so I just looking at the uh the quizzes and Johnny and Kim xerox's the wrong one so we're don't worry we're going to do them at the end so just oh you want it sooner yeah I can give you the wrong wrong quiz I've got the wrong one but it's harder no all right so hang it hang in there till the end say save your save your adrenaline Johnny and Kim are off off running as fast as they can and we'll be back with lots and lots of copies of the newer correct quiz all right so what I want to do what I want to do today is to talk about chapter 28 and chapter 28 is on amino acids peptides and proteins So Beautiful chapter beautiful topic fantastically important follows on the heels of carbohydrates the main classes of biomolecules are sugars proteins nucleic acids and then you throw a few lipids and secondary metabolites like alkaloids and and so forth on top of that and chapter 28 is a wonderful chapter in the sense it tries to cover everything and the result of course is given the limitations of the course if I don't cut cut it down we will cover nothing and so what I've decided to do is really focus Aman on amino acids and particularly peptides from the point of view of synthetic chemistry and not even so much the synthetic chemistry of amino acids there's some cool chemistry on the streker synthesis there's some interesting stuff in the chapter that overlaps with your biochemistry class on isoelectric points and other aspects of amino acids and and peptides and some of this you'll get in your biochemistry class but I really wanted to give you my own perspective on this topic and what I see is really some of the beautiful and profound aspects so let me start with a simple amino acid structure and then a simple peptide structure and so maybe maybe for regular amino acids meaning sort of typical amino acids maybe the amino acid Alan alanine is sort of the archetype it's an amino acid and people because the amino group is at the alpha position call these Alpha amino acids and as I said this particular one is called alanine it's the smallest amino acid with a side chain now amino acids of course have Amino groups and they have carboxy groups and so they can be connected together end to end and when you connect them together end to end you get a peptide small collections of amino acids containing oh up to about 40 amino acids end to end are typically referred to as peptides larger ones often in nature polypeptides have folded structures and are typically referred to as proteins there's not a hard and fast definition of where the boundary is between peptides and proteins but usually the the emphasis would be on folded structures of biological Origins for proteins so I want to draw out a simple tripeptide and I've just arbitrarily taken three amino acid IDs the first one is phenyalanine the second one is isoline and the third amino acid is Lucine in this chain so we call this a tripeptide because it's composed of three amino acids so peptide or a tri peptide and the particular name of this tripeptide if you want to get technical would be pheny allanal isol Lucine p h e n y l a l a n y l ISO Lucine all one word not not super important how you name how you name polypeptides polypeptides have attracted the attention of chemists for organic chemists for so so long because these are the molecules of life and because organic chemistry really is the science of life and its molecules and some of them are remarkably remarkably powerful so for example the polypeptide oxytocin was first elucidated the structure was first elucidated and then in a tour to force effort it was synthesized by Vincent de venod in 1953 and he immediately I mean time scale of Nobel prizes immediately won the Nobel Prize for it by 1955 so it's a Nona peptide that means nine amino acids and it contains a disulfide bond I'll just give you a cartoon of of the structure but I want to talk about it so I'm not going to even draw out all the nine amino acids in it the inter terminal amino acid the back end so this is called the inter terminal is ayine cysteine is like alanine but with a sulfur instead of a ch3 group and then you run through another four amino acids and then the molecule snakes back on itself whoops let me get the structure right here and again I'm sort of giving an abbreviated cartoon of the molecule we have another cysteine so another ch2s and the sulfurs can link together to give disulfide sulfur linkages if your hair gets frizzy or if you uncurl your hair with a curling iron or with straightening solution and then it locks back in with curls in it it's sulfur linkage is in your hair that actually lock lock in that structure CU of course hair is hair is protein all right and then we continue through another three amino acids and I'm not going to again draw it I'll just say 3 AAS to the C Terminus of the structure and it happens to have an amid group here and so I'll just write over here C Terminus so this peptide in addition to having this fantastic historic Importance of Being this sort of milestone in synthetic chemistry and a real Mark of achievement of What organic chemists can do also has remarkable biological properties this peptide is produced by your pituitary gland it's involved in uterine contractions in in pregnancy and in birth it's involved in lactation but incredibly this is also involved in emotions and pair bonding in other words love you know you say oh I'm in love with a person and it's that person and it's you in the end it's chemicals in your brain I mean this is real this is really scary you know it's not you it's the lack of oxytocin I feel for you my God what a what a deal what a deal breaker there's fascinating literature I don't want to get started out there on differences in monogamous Behavior among different species of VES you know these little creatures that run around on the ground like mice or shrews and the Prairie VES are monogamous they participate in pair bonding they hook up for life with a partner and it turns out out that ties into oxytocin and a related hormone vasopressin in its receptor levels so this is incredibly powerful stuff I'll give you one more example because this is a cool example of the types of things that we can synthesize right now so the virus HIV of course horrible horrible stuff the AIDS virus and one of the enzymes That's essential for its life cycle is called hiv1 protease and it's a 99 amino acid polypeptide protein it cuts the other proteins that are needed for the life cycle of the AIDS virus it's what these powerful drugs against age AIDS the HIV proteas Inhibitors work against their molecules that fit into this enzyme and gum it up so it can't cut the proteins that need to and this protein has been synthesized it's a dimer by the way meaning two halves come together non-covalently but this protein has been synthesized chemically in the laboratory and what's really cool okay so you'd say well great nature can make this thing too what's really cool is chemists can make the mirror image of the protein and have used that to discover drugs which is really really cool where you can go ahead and then use biological techniques to get a peptide that interacts with the mirror image and then you make the mirror image of the peptide that interacts and you've got something that biologically is functional but doesn't break down anyway incredibly cool stuff I'm just going to give you a little bit of flavor of things so there are 20 common naturally occurring amino acids people often refer to these as 20 natural amino acids natural is a little bit of a of a a fake word here because you can find others in nature but there are 20 that are regularly coded for in the proteins in your body I'll leave it to your classes in biology to insist that you memorize all of them or memorize the three-letter codes just like just like um like we did with the sugars where I focused on a few sugars I'd rather you know a few of them I'll put up more than I think you should know but I want to show you some some principles here and show you some of the variations so a lot of the amino acids have nonpolar side chain so for example we already saw alanine with a methyl group and that's kind of kind of the archetype for amino acids is to have a side chain if you have an alkal group as the side chain you describe it as a non-polar amino acid right you've got a greasy side chain grease and hydrophobic interactions the desire to get away of water from water are a big factor in protein folding so typically you have more of these hydrophobic amino acids on the inside of proteins there are all sorts not all sorts but quite a number of different alkal side chains so for example alanine is a methyl group veine is an isopropyl group phenyalanine is a benzo group Lucine is an isbut group I'll just draw out a few of these l c i n e all right so there are a couple of hydrophobic a couple of greasy amino acids that are sort of oddballs in structure glycine is actually the smallest of amino acids so glycine is the only one that doesn't have a side chain so all of the other amino acids have a side chain they all have the same direction of the side chain cysteine because of the conning gold prog rules they're all by the way s stereochemistry so I'll write s here with one exception the amino acid cysteine because of the higher coning gold prog priority of sulfur ends up being R even though the chain points in the same direction but that's kind of a technicality okay so this is glycine so glycine of course is a chyro we don't have a stereogenic Center at the alpha position the other sort of odd ball among the nonpolar amino acids is the amino acid Proline technically Proline gets called an amino acid but that's not particularly important what is important is that the amino group in Proline is a secondary amine rather than a primary Aman this gives rise to some interesting structural features in proteins proline in particular has a tendency to turn back on itself for example because you can get CIS and trans conformations about the amid group that it forms all right so that's kind of a a selection of some of the hydrophobic amino acids I want to show you some of the uh polar charged amino acids so the amino acid Serene for example has a hydroxy group one of of the reasons that we're doing this right now and why you're writing these out is that unless you go ahead and really see things unless you actually write and think about them all of this just ends up structures in black and white so Serene if you can't read my writing s r i n e is just like alanine but it has an alcohol group it has a hydroxy group off of the methyl position there's three anine as well which has an extra methyl on there but I won't write it out for you so I talked about cross lengths from sulfur and they're one of the important things in protein structure so the amino acid cysteine is just like Serene but it has a tho group it has a sulf fyro group and thol groups oxidize very well they oxidize very easily and form disulfide CR lengths and so this ends up as I mentioned before with hair and so forth giving structure to proteins not all of the amino acids have side chains that are neutral in water at physiological pH and again I will leave it to you and and uh and your biochemistry classes to discuss more the charge of amino acids at various conditions but this amino acid is glutamic acid you may have heard of it in terms of so mono sodium glutamate MSG in your food in Chinese restaurants it's the salt of it gives a meaty flavor to things and of course in water at neutral pH the carboxy group right carboxilic acids have a PK of four or five so in water at neutral pH you're going to have carboxy group deprotonated even if the amino acid is part of a polypeptide where the amino group and the carboxy group of What's called the main chain are part of the polypeptide the side chain is going to be deprotonated so glutamic acid is an acidic amino acid there are basic amino acids but I want to show you it's sister it's illn named sister I might add another polar Amino acid so we have a primary amid group here this is called glutamine glutamine is just like glutamic acid but with an nh2 group instead of a carboxy group with an amid group now to me that doesn't make any sense glutamine isn't an amine an AM group isn't an amino group it's not basic it doesn't behave like an amino group but that's its name and you call it that there are amino acids with real amine groups here lysine being one of them another basic amino acid and I'll give you one last amino acid as I said I'd say this is more more than I would expect you to know unless you're a practitioner of the art but you've seen now examples of all of these functional groups here and so I think this is a really really nice introduction to amino acid structure in polypeptide so lysine of course at physiological pH remember your PKA side chain of Lysine it's an AM PK is going to be about 10 or 11 so it'll be protonated at physiological pH arginine is the last one I'll show you also has a basic side chain it's got a guanidine group arginine is even a r g i n i n e Arginine the side chains even more basic than an amino group and so it's going to really be protonated at physiological pH at just about any pH you can imagine all right now as I as I was saying at the beginning what I think is just fantastic is the progress that chemists have made in the chemical synthesis of peptides and proteins and if you think about it the way in which one can investigate biological function for example the function of oxytocin or the function of vasopressin is to make molecules that have similar structures and say what does this group do do what does the cysteine group do what happens if we ar rearrange the structure and so the chemical synthesis in addition to being a way of initially proving structure also ends up being a a tremendously powerful ex exercise in investigating biology now the conundrum if you look let's take a simple dipeptide and so if I draw out just a simple dipeptide I'll say R2 for just a generic side chain and R1 for just a generic side chain and again that could be anything it could be phenyalanine it could be isoline it could be Lucine so if we look at this basic structure you say okay well it's pretty obvious that the main bond in a polypeptide is an amid Bond you can say okay it makes sense if we were to think about how to make this molecule we'd look at that Bond and say we've learned a heck about making amid bonds we've been talking about carboxilic acid since the beginning of the of course in chapter 19 and then some more about it in chapter 22 we look and say from a strategic point of view this is really simple you go and say all right we just have to Envision making that amid Bond and you know in the abstract in the view at 20,000 ft that we can make an aid bond by the reaction of a carboxilic a acid and an amine and now the problem begins well how do you actually how do you do this we've learned lots of chemical reactions we've learned that under the right conditions if you go ahead and mix a carboxilic acid and an amine maybe with a coupling agent you learned about DCC for example you say we've learned ways of making amid bonds you look at this and you say yeah okay maybe somehow we could Envision putting this putting this together but obviously obviously you've got fantastic problems here you've got two different carboxy groups two different Amino groups even if I threw together one amino acid and the other amino acid with something to make the carboxy group react with the amino group you've got a molecule could react with itself you could get a molecule with two r1s in it or two r2s in it or an R2 at the nend at the C Terminus and an R1 at the end Terminus or the molecule could continue to build a polymer and you get three or four in other words you'd get an Unholy mess no matter what you do and we've been talking for the entire class about how organic chemistry is all about control and how organic chemists seek to control how reactions occur and that really boils down to being the essence of the synthesis of peptides and proteins so imagine for a moment I'll show you the the answer and then we can talk about sort of the the wise and so forth imagine for a moment we took one of of our components and we were to tie up we were to protect the amino group here we've already learned about the concept of protecting groups you've learned for example when you have an alcohol that you don't want to react as an alcohol you can mask it you can protest protect it as a tbdms ether a tbal dimethyl ether group and you've learned that carboxilic acids don't react like carboxilic acids when they're part of an Esther group so you could Envision protecting the carboxy group as well and so by being able to selectively protect to tie up the amino acids you can achieve this element of control the groups that are widely used for these types of protection reactions are various Esters including benzil like Esters benzil and benzil related Esters for the carboxy group and the tach T butoxy oxy carbom and other carbamate groups for the amino group let me show you a specific example of just a standard way of putting together peptide we'll make Veo alanine by this so imagine for a moment now that we put on on veine your textbook will talk in more detail about how these protecting groups can be introduced I think in the time in the time we have I'll simply say it's very easy to take the amino acid veine and reacted with a reagent like dibal dicarbonate to go ahead and put on a boach group on the end Terminus of it and by various esterification processes one can go ahead and put on a Benzel ether or a Related Group to a Benzel ether on the C terminal group and I think I said we're going to use ve alanine here so I will just go ahead and point out that this is BN is used to abbreviate benzil group and we've learned about reagents that can react with a carboxy group and render it more reactive so for example the reagent DCC I'll show you it in just one second can go ahead and can activate this carboxy group and then allow it to react with this amino group so the overall product of this reaction action and I will now start to use shorthand for these very big molecules the overall product for this reaction then is the bach Amino veine on the end Terminus Ozil eser on the sea Terminus and I haven't drawn the byproduct of DCC all right so just to reduce things and we're going to have to reduce things to a lot of our groups let's imagine for a moment that this caroal group is the caroal group on that carboxilic acid that Bach viline carboxilic acid DCC is a diid reagent we talked about it briefly your textbook gives a mechanism for its reaction it's really not the best way of writing the mechanism but I think many students would think of the mechanism in the way you're textbook react writes it suffice it to say cyc DCC D cyclohex carbo diid can react with a carboxy group to give an activated carboxy group and the structure that I'm drawing here looks awfully fancy until you think about it I'll abbreviate those cyclohex as see y this structure looks awfully fancy until you think about it and then you say wait a second for the longest time he's been saying that a double bond to nitrogen is very similar to a double bond to oxygen so this structure this intermediate this oil Ura intermediate I'll just abbreviate as int is basically like an anhydride in other words we have a carbonal with an electron withdrawing group on the oxygen and so the amine partner which in this case I will just abbreviate as R Prime nh2 now con act that of course being the uh the uh uh cbz Esther of alanine there or rather the Benzel eser of alanine alanine Benzel eser can react I won't take us through all all of the steps of the mechanism but suffice to say the first step of the mechanism is the amine nucleophile can attack the carboxy group of the oil Ura intermediate electrons kick up on the oxygen electrons kick down they kick out what ultimately is D cyclohex Ura after some proton shuffling and so the product of this reaction is the amid plus the byproduct D cyclohex Ura and as I've been emphasizing in this class organic chemists are very bad about writing byproducts of reaction because they're typically focused on the main product the byproduct is called DCU dyc hexal Ura so DCC by the way was the first major coupling reagent that was invented but it wasn't the last it's actually terrible stuff to work with it reacts with the proteins in your body to functionalize them which sets your immune system on guard against them which means that after working with it for a while you'll start to develop terrible terrible rashes which is why Johnny and Kim even though they will synthesize peptides in the laboratory as part of their research on cancer and Alzheimer's disease never work with DCC all right so so here we are at our peptide and I want to draw out the structure again and talk about what can happen to this because now we have a peptide we've synthesized a peptide in which our C and N Terminus are protected with protecting groups the Benzel group on the Benzel Ester group on the o on the C Terminus the bach group on the N Terminus the bach group is labile to acid that means that a strong acid can take off the bach protecting group and return to you an amine or technically an amine salt that can be deprotonated the Benzel group is labile to among other things hydrogenolysis it's also laile to very very strong acid like hydrogen bromide and anhydrous acetic acid so if we take our dipeptide and we carry out two deep protection steps on it a hydrogen a um we'll start with a uh a triotic acid deep protection step this is TFA I'll write this in parentheses triotic acid is a pretty strong acid it's right on that cusp between weak acid and strong acid not as strong as HCL not as strong as sulfuric acid its PKA is about3 so it's way way stronger than a regular carboxilic acid due to the inductive effect of the trio methyl group and then if we carry out a hydrogenation with padium on we can remove both of the protecting groups and so I'll I'll just remind us I'll say B is able to be removed with strong acid EG for example TFA and the benzil group is able to be removed by hydrogenolysis or very strong acid and as I said by very strong acid I mean for example Hydrochloric acid HCL in dioxine hydrogen chloride in dioxine or um or hbr and acetic acid all right so the overall result of this is that we have now removed both of the protecting groups to give us just the free peptide like so in other words we have hidden one carboxy group hidden one amino group brought together the other carboxy group and the other amino group and coupled them together now I'm lying to you just a hair about this because I haven't used a base technically will still be the TFA salt I'll say it's still the TFA salt at this point but honestly if you wanted the free base you could just go ahead and and add a base anyway so technically still the TFA salt all right I want to show one thing we're kind of taking a trapes through mechanism here but sort of mechanism light and getting getting kind of a summary of how things work we've taken certain mechanisms in the course and work them over in gruesome detail like acetal formation and acetal hydrolysis which came back to us in sugars we're getting others where we're getting the general gist of it let's talk about the bach de protection mechanism so okay so here you have your boach group like so oops now in a in strong acid like TFA you can protonate all the different positions in the bach group and the easiest way to think about taking off the bach group is if we Pro protate on this nitrogen here so I'll write this sort of as a transient intermediate if we protonate on this nitrogen here now we're all set up to lose a tbal carbocation and so if we just go ahead and kick out electrons we're going to fragment this molecule into carbon dioxide carbon dioxide is very stable andb carbocation and an amine like so and then of course as I was hinted at over here your amine I'll just draw this down here with more TFA will go to RNA will protonate to give the ammonium salt like so all right [Applause] so I want to point out a couple of amino acids that are special we've already seen them so we saw for example with lysine you have an extra amino group and we saw with glutamic acid that you have an extra carboxy group and so in these amino acids and in several of the other functionalized amino acids amino acids with a acidic and basic and polar side chains additional protecting groups are needed and suffice it to say there's chemistry to put on these protecting groups and I want to stop at this point talking about the details of protecting groups and come on a little bit more to the theory of what we do so okay so the general gist of things is we're going to build our peptide amino acid by amino acid starting at the C Terminus and working to the end terminus in other words you could imagine with the veil alanine that we made if we had for example only taken off the bach protecting group off of the amino Terminus we could then go ahead and couple in another amino acid say phenol Alan another amino acid say phenyalanine to make a tri peptide we would introduce that feny aladine by having a Bach group on the amino Terminus on the amino group and a free carboxy group and again carrying out a uh a DCC coupling reaction and so this is the type of technology that allowed Vincent of VOD to build up to synthesize the Nona peptide oxytocin back in the 1950s and ultimately really create the beginning of a revolution now another huge Advance came along with an idea that Bruce marfield introduced in the 1960s and his colleagues thought he was crazy for this but he won the Nobel Prize in 1984 for what he did and his idea was to go a head and connect the polypeptide to a solid support in other words to make the C Terminus of the polypeptide instead of just a protecting group a big plastic bead and so let me show you the gist of modern solid phase peptide synthesis and then we can run through a few of the details so imagine for a moment that we have a polymer bead polymer plastic polystyrene I'll show you the structure in a moment and it's not exactly what marfield initially used but imagine for a moment that the polymer is basically a big benzil alcohol and that you have an O group on there and then in the first step we couple one amino acid I'll call it sort of in the abstract we'll just call it R1 for our side chain and we'll say that we have a protecting group on the nitrogen so this would be like a buck protected amino acid and so now we have our amino acid with our protecting group I'm just calling that PG onto the resin and I'll abbreviate the polymer with this big ball here all right now imagine for a moment that we deprotect in other words we carry out a reaction like the TFA reaction to remove that protecting group for example to remove the bach group that was introduced at this point you're going to get a you're going to have the amino group here the free amino group connected to the first amino acid connected to the resin which I'm a abbreviating as a circle now imagine for a moment that I couple in the next amino acid and so I'll say I'll couple and we'll call this R2 on an amino acid again with a protecting Group which I will call PG and I think I'll move down to the Blackboard here to show you what we've now got so now we have our two connected and now we have our protecting group and imagine for a moment that we again depr protect and now I'm going to shorten things and write de protect this step one and couple and I'll show you our third amino acid you notice that we're starting at the C Terminus and we're building up toward the end Terminus so I'll call this R3 and our structure is getting so big that I now have to go to the other Blackboard and at this point we're at a tripeptide now attached and I've gone from the N Terminus to the C Terminus here with our third residue our second residue and our first residue and finally imagine if in the abstract we cleave from the resin and we deprotect I'll say cleave and deprotect because they're sometimes done at the same time and the result of all of that now is that we have synthesized a tripeptide and the operation is so simple once you work out the the chemistry that it can be done on a machine repeating these operations one after another after another to build up polypeptides and even very small proteins purely through chemical synthesis and this was what got marfield the Nobel Prize it was this recognition that you could do this and the achievement of doing it and so while the work of synth izing an ox oxytocin a Nona peptide was a fantastic tour to force this opened the job to make things trivial to make molecules of that size and one of the beauties of this is you really need your Chemistry to work cleanly and so you can use a huge excess of reagents for equivalents of each amino acid to drive the chemistry question why is this um from C to n ah great question why are we going from C to n and that question is particularly profound when it is counterintuitive when on the ribosome you synthesize it or the ribosome synthesizes the protein from n to C it turns out that there are reactions that occur if I try to activate let's even assume I had this protecting group and I tried to activate this carboxy group with DCC there are reactions OCC that occur that will epimerize this stereo Center in chemical environments with vigorous activating agents like DCC so you will get a mixture of diamer so in general like all the time with certain very special exceptions including something called native chemical liation that may give rise to the next Nobel Prize in this area with certain exceptions with with virtually no exceptions I should say we always go from C to n the opposite of the way of the ribosy all right I want to show you a couple of last bits of the genius that was involved in all of this this chemistry so one of the pieces of Genius is really very simple it's the polystyrene so polystyrene is a polymer in which you have a zigzag chain of polyethylene with Benzene Rings attached like so you make it by polymerizing the Aline styro linking the molecules together one after the next after the next now styrene is styrofoam if you've ever taken Styrofoam peanuts and put them in any organic solvent like acetone they form a big goo if you do this with a styrofoam cup that you bring into lab and you put a little acetone in there it just melts it just dissolves technically so merrifield's bright idea one of his bright ideas was to link together two chains with a little bit of divinyl benzene to Crosslink the polystyrene into a big Network like so so that the chains all link together and the molecule would swell up but it wouldn't Des disolve and then he used the Benzene ring and functionalized just a few of the Benzene rings on the polystyrene to put on the protected amino acid with the protecting group so that was one one real piece of Genius here and so the chemistry that I've sort of been outlining here really can be thought of as I'll write this as Bach let's say for the the one that we or one that we could synthesize Bop polystyrene and then we can follow with a series of De protection and coupling steps where we use TFA triotic acid to deprotect the amino group and remember I said well your amino group technically is still protonated so you can add a base like diisopropyl ethylamine or triethylamine to deprotonate I2 NE to deprotonate the amino group that's now liberated and three will couple in the next amino acid and so I'll say Bach Fe Fe is the abbreviation for phenol alanine so I'll say Bach F and DCC and now we can get Bach Veil Bak Fe Veil Ops and we can repeat and repeat and repeat to build up the polypeptide chain one amino acid after the next after the next so I will I think I think leave you with well let me let me uh go ahead and I'll I'll just say repeat and let's say I did this this time with alanine so again it's we we shorthand a lot of a lot of stuff here so let's say I I go ahead and do this with um let's say Lucine so repeat and now we go Bach l v Veil Ops and now if you imagine we use a very very strong acid now we can get a tripeptide and if we had continued on the resin we could have gone up to tetrapeptide all right the final Innovation that I want to show you and this is realized this is standing on the shoulders of giant for many years who've made this chemistry possible to a point where it is now routinely possible to make peptides and small proteins so one of the last Innovations was Mara Field's initial chemistry was kind of nasty and by nasty I mean that that last step of deprotecting of getting rather cleaving from the resin getting the amino acid off of the resin getting the polypeptide I should say off of the resin required super super strong acid hbr hydrogen bromide and acetic acid is one of the reagents use just nasty stuff anhydrous hydrocloric acid anhydrous HF eats through glass Burns through skin burns to your bone does horrible horrible stuff and so the last innovation that I'll introduce was a base labal protecting group The F group and the fmck group is a big big big aromatic unit it stands for it's in the same family as the boach group it's a florino methyl that means ch2 oxyc carbon Neo and the FM group is cleaved with a base such as peridine so I'll say a mild the mean base and so the F group if you treat it with pyodine whoops the base can pull off a proton here kick out an alen over here kick out an oxygen and ultimately kick out carbon dioxide so when this occurs now you end up with the bh+ the protonated base plus the group that came from the floral Group which eventually reacts with some more base plus CO2 plus the Amine and so putting all of this together I'll just show you an example of a modern solid phase peptide synthesis and then we'll wrap things up so in a modern peptide synthesis what's done is the polystyrene is linked to a much more acid labile Linker and this might be a good final exam question to go ahead and explain why this Linker here is much more labile to acid and now you have your first amino acid oops that's a wedge here and so now we go ahead and I'll call this R1 and so we go ahead and we deprotect with peridine I'll just abbreviate that as pip and then we couple and as I said typically noway people don't use DCC but I will write DCC so here's our F protected second amino acid R2 and so now you build and build and build and this Linker here is called a wang Linker and so I will write o Wang PS and finally after building and building and building you'll cleave with pyodine and so I'll just say repeat repeat repeat and then you finally cleave with peridine I'll write that as pip and two TFA which cleaves the peptide off the W Linker to give your peptide all right well on that note we're going to take a moment to pass around the quizzes so take one minute to finish up writing and then you can put away your notebook