[azmanam]

It's the protons around 8ppm which concern me.  The rest of the structure looks more or less plausible.  The large signal around 7ppm is the 5 protons in the benzyl C-protection... but there's no reason there should be two signals around 8ppm. 

The other part that concerns me is the 4-5 region.  These should be the alpha protons between the C=O and the N for each amino acid.  There are 4 amino acids in this chain, so there should be 4 protons here.  Scaling up the integration values between 4-5ppm gives, from left to right, 2H, 1H, 1H, 2H, 1H.  The 2H signal on the left is the two protons between the N-terminus and the benzene ring.  That leaves 5 protons to account for.  But there are only 4 amino acids.  IMHO, there is one too many protons in this region.

The aliphatic region (1-3) is too messy to analyze, but a nice COSY spectrum would help.

IMHO, not the right structure... or at least not a clean sample.

[discodermolide]

It's the protons around 8ppm which concern me.  The rest of the structure looks more or less plausible.  The large signal around 7ppm is the 5 protons in the benzyl C-protection... but there's no reason there should be two signals around 8ppm. 

IMHO, not the right structure... or at least not a clean sample.

They are probably some of the NH protons, I can't read the intensity on this picture, it's too small for my bad eyes!

[azmanam]

I dunno...  I guess.  But only 2, not 4? They look too regular and sharp for me.  Almost like a plasticizer or some such impurity.

[molecule_787]

I have included the NMR from another supplier.  These are two separate "PSI" peptides/compounds produced by two separate labs.  The structures to the "untrained" eye appear quite similar with the exception of the missing Aldehyde which appears to show up in between the 9 - 10 ppm in the NMR report from Lab B (as several of you stated it should).  

Any comments on the similarities or differences would be most appreciated.  Is Lab B's compound of any significant difference?  If so, does it appear to be the correct structure of the desired Tetrapeptide Aldehyde PSI, posted at the top of the thread?  I have also included the Mass Spec from Lab B which appears to be on target with the Mass weight of the peptide which is 618.77 and Lab B's peptide peaks on the Mass Spec report at around 619.5.

Still trying to seek out an NMR that was done on the original PSI peptide for further comparison.

LAB A (CHINA) NMR REPORT




LAB B (USA) NMR REPORT



LAB B (USA) MASS SPEC REPORT




Any insight regarding the above reports and their relation to the correct PSI structure is again appreciated.  Thank you.

[azmanam]

Who integrates these spectra!

[molecule_787]

Not only the aldehyde signal. Structure and spectrum does not fit somehow.
I would do LC-MS additionally.
I see a Z group and Boc, but the rest is a bit strange.
There are some companies outside which sell crap. Especially when they offer a very cheap price.

The Merck price is realistic. 3k for 1g seems a bit too cheap since these companies will make it (synthesis after request). No one will store large amounts of a (sensitive) peptide. I know what I write, I work for such a CRO company.
They should provide a proper NMR and LC-MS at least. When it fits you can order it. I would only pay after analyzing this stuff soon after receiving it.
I´m sure half of the providers will not answer to your spectra-request. This will separate the boys from the men.

Where are these labs from you ordered situated? China?

Yes, they have only done the synthesis to order but of course we require HPLC, NMR and Mass Spec to confirm correct structure and purity before shipping and payment.  Also have a third party lab set up to re-test the delivered product if the HPLC, NMR and Mass Spec check out from the original labs.

LAB A is based in China

LAB B is based in the USA

I know you know your stuff and I respect your insight and opinion very much, hence why I am here.

[discodermolide]

I dunno...  I guess.  But only 2, not 4? They look too regular and sharp for me.  Almost like a plasticizer or some such impurity.

I think they are broad doublets, although with my eyes !!! Plasticiser is a bit further unfilled in the alkyl region?
Someone needs to do a D2O exchange on this sample.

[molecule_787]

I dunno...  I guess.  But only 2, not 4? They look too regular and sharp for me.  Almost like a plasticizer or some such impurity.

I think they are broad doublets, although with my eyes !!! Plasticiser is a bit further unfilled in the alkyl region?
Someone needs to do a D2O exchange on this sample.

What are your thoughts specifically on the two different NMR's from the two different suppliers on two different peptides?  Does the US lab appear to be the correct structure in your opinion? 

[discodermolide]

I dunno...  I guess.  But only 2, not 4? They look too regular and sharp for me.  Almost like a plasticizer or some such impurity.

I think they are broad doublets, although with my eyes !!! Plasticiser is a bit further unfilled in the alkyl region?
Someone needs to do a D2O exchange on this sample.

What are your thoughts specifically on the two different NMR's from the two different suppliers on two different peptides?  Does the US lab appear to be the correct structure in your opinion? 

At least you see the aldehyde signal, although the resolution does not seem to be so good. Run a reverse phase HPLC to check out both samples.

[OC pro]

Seems Lab B has done a proper job. NMR does not look nice but correlates with the structure and taking also the mass-spec into account I´m convinced.
Lab B is the winner  

[discodermolide]

Seems Lab B has done a proper job. NMR does not look nice but correlates with the structure and taking also the mass-spec into account I´m convinced.
Lab B is the winner  

I fail to see why the could not get the spectrum in phase and get a better resolution. I would not accept this from my co-workers. It looks as if lab B has the correct structure.

[OC pro]

Yeah I would not send such a crude spectrum too. Seems their Quality Management is not working properly

[molecule_787]

Yeah I would not send such a crude spectrum too. Seems their Quality Management is not working properly

^You are referring to the "unpolished" LAB B report/paperwork, correct?  

When you say LAB B has done a proper job but the NMR does not look nice I assume you are simply referring to just the quality/resolution of the paperwork/report.  I did ask/inquire about this also and was given an apology along the lines of it being substandard and that the issue will be addressed internally et.

So the consensus is that LAB B has done a correct job, the peptide is clean and the structure is correct as per NMR and MS.  So LAB B seems to be the better choice and more importantly, a legitimate one.  

The USA based lab as oppose to the China...

Just a FYI, the HPLC came back at >98% for LAB B and only around 91% for LAB A but LAB A stated that they could try and bring up the purity to 98% et.  We require a minimum 98% purity.

[OC pro]

According to that NMR which lab B sent, this compound is far from being >98% pure. They should really provide a much better NMR. This one is a joke.

[arit]

Somehow neither of those spectra manages to convey the message "freshly measured from the stuff we sent/will send you".