Source of Crude peptide

{{Infobox concept | name = Crude peptide | subtitle = Process intermediate | Obtained from = [[Resin cleavage|Cleavage]] of the assembled chain | Typical purity = Highly variable; sequence-dependent | Principal impurities = Deletion and truncated sequences }} '''Crude peptide''' is the material obtained immediately after [[Resin cleavage|cleavage]] from the solid support, before any chromatographic purification. It contains the target peptide together with every by-product that accumulated during assembly and cleavage.{{r|behrendt2016}} Its purity is highly variable and is largely determined by sequence. An easy 10-residue sequence may cleave at high purity; a difficult 40-residue sequence may cleave at well under half. That figure sets the cost and difficulty of everything that follows.{{r|behrendt2016}} Crude peptide is sold as such in some markets, principally where the purchaser intends to purify it. Material described only as "crude" is not a defective product; it is an intermediate, and describing it accurately is what distinguishes it from a purified one.{{r|usp1503}} == What is in it == The dominant impurities are sequence-related: deletion sequences missing one or more residues where a coupling failed, truncated sequences where a chain was capped, and any peptide bearing residual protecting groups where cleavage was incomplete.{{r|behrendt2016,merrifield1963}} Cleavage adds its own. Strongly acidic conditions release reactive cations from the protecting groups, which can alkylate tryptophan, methionine and cysteine unless scavengers capture them; oxidation and, for susceptible sequences, aspartimide formation also occur. Non-peptide material is present too: scavengers, residual cleavage reagent, and trifluoroacetate. A crude figure quoted as a percentage is normally a chromatographic [[Area percent purity|area percent]], so it says nothing about how much of the solid is peptide at all. See [[Peptide content]].{{r|usp1503}} == From crude to purified == [[Preparative HPLC purification|Preparative chromatography]] separates the target from the closely related impurities, and the yield of that step falls as crude purity falls: more material must be discarded to reach a given specification.{{r|behrendt2016}} |+ How crude purity governs the purification burden{{r|usp621}} | Crude purity | Consequence for purification | |---|---| | High | Narrow fraction cut; good recovery | | Moderate | Wider separation problem; recovery falls | | Low | Several passes may be required | This is the mechanism behind the observation, made at [[Preparative HPLC purification]], that the cost difference between 95% and 99% material is not proportional to the difference in the numbers. It also bears on identity. A crude containing a high proportion of deletion sequences is a crude in which the main peak is less dominant, and identity confirmation by [[Mass spectrometry|mass]] becomes correspondingly more important rather than less.{{r|usp1503}} == Crude material in the research market == Where crude material is offered, the honest description is that it is unpurified. Documentation for such material should say so, and a certificate reporting a high purity figure for something described as crude is internally inconsistent.{{r|usp1503}} The reverse risk is more consequential: purified-grade documentation attached to crude material. No analytical determination distinguishes the two by name — the question is simply what the chromatogram shows — which is why an itemised related-substances profile is more informative than a headline figure. This is a documentary observation about how material is described, not an allegation about any supplier. Material honestly described as crude and priced accordingly is an ordinary product with an ordinary use.{{r|behrendt2016}} == References == {{reflist}} <ref name="behrendt2016">Behrendt R, White P, Offer J. "Advances in Fmoc solid-phase peptide synthesis." ''Journal of Peptide Science'' 22(1):4–27 (2016). PMID 26785684.</ref> <ref name="usp1503">United States Pharmacopeia, General Chapter <1503>, ''Quality Attributes of Synthetic Peptide Drug Substances''.</ref> <ref name="merrifield1963">Merrifield RB. "Solid phase peptide synthesis. I. The synthesis of a tetrapeptide." ''Journal of the American Chemical Society'' 85(14):2149–2154 (1963). DOI:10.1021/ja00897a025.</ref> <ref name="usp621">United States Pharmacopeia, General Chapter <621>, ''Chromatography''.</ref> == See also == * [[Solid-phase peptide synthesis]] * [[Preparative HPLC purification]] * [[Resin cleavage]] * [[Area percent purity]] * [[Peptide content]] {{DEFAULTSORT:Crude peptide}} [[Category:Peptide synthesis]] [[Category:Purification]] [[Category:Manufacturing and supply]]