Phthalimidooxy-dPEG®4-NHS ester, product number 10011, is a protected aminooxy compound linked to an amine-reactive N-hydroxysuccinimidyl (NHS) ester through a 17-atom (19.0 Å) single molecular weight, discrete polyethylene glycol (dPEG®) spacer. This allows a hydrophilic, protected aminooxy group to be installed on peptides, proteins, small molecules, and amine-functionalized surfaces.
NHS esters are the most commonly used active esters for reacting carboxylic acids with primary or secondary amines to form stable amide bonds. They are unstable in aqueous media. At high pH values, the half-lives of NHS esters in water are measured in minutes. However, at physiological pH ranges (7.0 – 7.5), they have excellent reactivity and sufficient hydrolytic stability for bioconjugation purposes.
The phthaloyl moiety on phthalimidooxy-dPEG®4-NHS ester stably protects the aminooxy group. Because of the conditions needed for deprotection of the aminooxy group, the NHS ester end of the molecule must be reacted first. Following amide bond formation, the phthalimide group can be removed using aqueous hydrazine, leaving the aminooxy group free to react.
Oxime bonds form from the reaction between an aminooxy group and an aldehyde or ketone. If the formative reaction is between an aminooxy and an aldehyde, the oxime bond formed is called an aldoxime. The oxime bond formed by reaction of an aminooxy and a ketone is called a ketoxime. Compared to hydrazone bonds, oxime bonds are exceptionally stable. They do not break under physiological conditions or even slightly acidic conditions that can occur under some physiological states.
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Hermanson, G. T. Chapter 3, The Reactions of Bioconjugation. Bioconjugate Techniques, 3rd edition. Academic Press: New York, 2013, pages 229 – 258, particularly pages 233-234 (NHS esters), and pages 251-252 (aldehyde and ketone reactions). Want to learn more about Greg’s book? Click here for a review of Greg’s book and a link to purchase it.
Hermanson, G. T. Chapter 5, Homobifunctional Crosslinkers. Bioconjugate Techniques, 3rd edition. Academic Press: New York: 2013, pages 275-298, especially pages 277-278, discussing NHS esters.
Hermanson, G. T. Chapter 17, Chemoselective Ligation; Bioorthogonal Reagents. Bioconjugate Techniques, 3rd edition. Academic Press: New York, 2013, pp 757-786, particularly pages 763-766, discussing aminooxy-aldehyde reactions.
Hermanson, G. T. Chapter 18, PEGylation and Synthetic Polymer Modification. Bioconjugate Techniques, 3rd edition. Academic Press: New York, 2013, pages 787 – 838. Quanta BioDesign’s dPEG® products are discussed extensively in this chapter!
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