Monday, February 14, 2011
Amino Acid Milk
In chemistry, an amino acid is a molecule containing both amine and carboxyl functional groups. In biochemistry, this term refers to alpha-amino acids with the general formula H2NCHRCOOH, where R is an organic substituent. In the alpha amino acids, the amino and carboxylate groups are attached to the same carbon, which is called the α–carbon. The various alpha amino acids differ in which side chain (R group) is attached to their alpha carbon.
Adding Amino Acids
An amino acid is coupled to the deprotected N-terminal amine of the resin, or previously coupled amino acid, using a coupling mixture such as the protected amino acid (3 eq), PyBOP (3 eq), HOBt (3 eq), and DIPEA (6 eq) in 1:1 DCM:DMF until the resin is negative to ninhydrin. Another popular set of coupling conditions is amino acid (4.4 eq), HBTU (4 eq), and DIPEA (8 eq) in DMF.
In the structure shown at the right, R represents a side chain specific to each amino acid. The central carbon atom, called Cα, is a chiral central carbon atom (with the exception of glycine) to which the two termini and the R-group are attached. Amino acids are usually classified by the properties of the side chain into four groups. The side chain can make them behave like a weak acid, a weak base, a hydrophile if they are polar, and hydrophobe if they are nonpolar.