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AAPPTec Fmoc Amino Acids
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Fmoc Amino Acids - History
By the early 1990s, Fmoc amino acids were as popular as Boc amino acids for peptide synthesis. The Fmoc amino acid protecting group was developed by Carpino in 1970 (Carpino and Han, J. Am. Chem. Soc. 1970, 92, 5748-9), and he soon developed solid phase peptide synthesis protocols utilizing Fmoc amino acids. The strong UV absorbance of the Fmoc amino acids and the Fmoc cleavage byproducts allow solid phase peptide synthesis reactions to be easily monitored by photometry. In the late 1970s, automated peptide synthesizers with reaction monitoring capabilities based on measuring Fmoc absorption were introduced. In spite of their high cost, Fmoc amino acids gained popularity. By the 1980s, Fmoc amino acids were very popular. Adding to the popularity of Fmoc amino acids in solid phase peptide synthesis is that TFA-labile resins could be used, thus eliminating the need to utilize HF and special HF cleavage equipment. As the popularity and use of Fmoc amino acids increased, prices of Fmoc amino acids dropped. Since then, Fmoc amino acids have quickly become one of the standards for solid phase peptide synthesis.
Fmoc Amino Acid Deprotection
The Fmoc group of Fmoc amino acids is acid stable but is removed with a base through a β-elimination reaction. The Fmoc group of Fmoc amino acids is less labile to primary amines than secondary amines, thus minimizing premature Fmoc deprotection by the N-terminal amine of the deprotected peptide intermediate. Fmoc amino acids are typically deprotected using piperidine, which also scavenges the reactive dibenzofulvene byproduct of Fmoc cleavage. In cases of sluggish deblocking of Fmoc amino acids, DBU may be used to remove the protecting group with added piperidine to scavenge the dibenzofulvene byproduct. DBU promotes aspartimide formation, and it should be used cautiously when the peptide contains aspartic acid residues. Alternatively in difficult sequences, using piperidine/DMF (1:4) with mild heating at 45°C can be effective (B.D. Larsen, A. Holm, Int.J. Pept. Protein Res., 1994, 43, 1).
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Fmoc Amino Acid OPfp Esters |
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Many common Fmoc amino acids are also available as preactivated Fmoc amino acid OPfp esters. Fmoc amino acid OPfp esters can couple to form amide bonds without additional activation, making them convenient to use and reducing epimerization produced by activation.
Standard Fmoc Amino Acids Deprotection Protocol
1. Place the resin in a round bottom flask and add 20% (v/v) piperidine in DMF (approximately 10 mL/gm resin).
2. Shake the mixture at room temperature for 2 minutes.
3. Filter the resin.
4. Add 20% (v/v) piperidine in DMF (approximately 10 mL/g of resin).
5. Shake the mixture at room temperature for 5 minutes.
6. Filter the resin and wash it several times with DMF.
Fmoc Amino Acids Deprotection with 2% DBU
1. Dissolve 2g of DBU in 50 mL of DMF or NMP. Bring to 100 mL.
2. Add 2% DBU solution (approximately 10 mL/g of resin).
3. Shake the mixture at room temperature for 3 minutes. Filter immediately.
4. Add 2% DBU solution (approximately 10 mL/g of resin).
5. Shake at room temperature for 5 minutes. Filter immediately.
6. Wash the resin several times with DMF or NMP.
Fmoc Amino Acids Deprotection with 1% DBU, 20% Piperidine
For difficult deprotections:
1% DBU, 20% Piperidine Fmoc Amino Acid Deprotection Reagent
Dissolve 1.0 g of DBU and 20.0 ml of piperidine in 50 mL of DMF or NMP, then bring to 100 mL.
Fmoc Amino Acids - Deprotection Procedure
1. Place the resin in a round bottom flask and add deprotection reagent (approximately 10 mL/gm of resin).
2. Shake the mixture at room temperature for 2 minutes.
3. Filter the resin.
4. Add deprotection reagent (approximately 10 mL/gm of resin).
5. Shake the mixture at room temperature for 2 minutes.
6. Filter the resin and wash it with several portions of DMF.
AAPPTec top quality Fmoc amino acids are affordably priced, and they are available in a variety of convenient sizes. Click here to view all Fmoc-L-Amino Acids from AAPPTec.
For Fmoc-D-Amino Acids available from AAPPTec, click here.
For Fmoc Amino Acid OPfp Esters available from AAPPTec, click here.
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