1. Chirality in microcystins
T Krishnamurthy J Am Soc Mass Spectrom. 1994 Aug;5(8):724-30. doi: 10.1016/1044-0305(94)80004-9.
A new method has been developed to identify the isomers of amino acids by derivatization of the corresponding standards with 1-fluoro-2,4-dinitrophenyl-5-L-alanine amide (Marfey's reagent or FDAA) and analysis of the diastereomeric derivatives by a liquid chromatography-thermospray mass spectrometry technique. Quantification of the FDAA derivatives that originate from standards was possible by using L-phenylalanine as the internal standard. The procedure was applied to determine the chiralities of the amino acids present in some previously uncharacterized blue-green algal peptides (microcystins).
2. The intrinsic helix-forming tendency of L-alanine
J Vila, R L Williams, J A Grant, J Wójcik, H A Scheraga Proc Natl Acad Sci U S A. 1992 Aug 15;89(16):7821-5. doi: 10.1073/pnas.89.16.7821.
Conformational energy calculations have been carried out for three hexadecapeptides in water--namely, a copolymer with the sequence acetyl-AAAAKAAAA-KAAAAKA-amide, 3K(I), in both the charged and neutral forms; a neutral peptide with the sequence acetyl-AAQAAAAQAAAAQAAY-amide, AQY; and a 16-residue L-alanine homopolymer with acetyl and amide terminal groups. The conformational energy was a sum of the empirical conformational energy program for peptides (ECEPP/2) potential energy plus continuum hydration free energy. An empirical (JRF) parameter set was used for the hydration free energy, together with an electrostatic contribution to the solvent effect from charged lysines. The computed relatively high helix content of the most probable conformation of charged 3K(I) and the intermediate helix content of AQY agree reasonably well with experimental values. The computed very low helix content of the alanine homopolymer agrees with experiments on block copolymers and on host-guest random copolymers. The calculations suggest that the high helix content computed for 3K(I) is due to the sum of internal and hydration free energies of the lysine residues rather than to a high intrinsic helix-forming tendency of alanine. The principal component lowering the computed helix contents of AQY and the alanine copolymer relative to 3K(I) is hydration.
3. Double axial chirality promoted asymmetric [2,3] Stevens rearrangement of N-cinnamyl L-alanine amide-derived ammonium ylides
Eiji Tayama, Noriko Naganuma, Hajime Iwamoto, Eietsu Hasegawa Chem Commun (Camb). 2014 Jul 4;50(52):6860-2. doi: 10.1039/c4cc02536a.
The base-induced asymmetric [2,3] Stevens rearrangement of N-cinnamyl tetraalkylammonium ylides derived from L-alanine amides proceeds via a double axially chiral intermediate to afford the corresponding α-substituted alanine derivatives with high enantio- and diastereoselectivities.