1.Diorganotin(IV) complexes of dipeptides containing the alpha-aminoisobutyryl residue (Aib): preparation, structural characterization, antibacterial and antiproliferative activities of [(n-Bu)2 Sn(H(-1)L)] (LH=H-Aib-L-Leu-OH, H-Aib-L-Ala-OH).
Katsoulakou E1, Tiliakos M, Papaefstathiou G, Terzis A, Raptopoulou C, Geromichalos G, Papazisis K, Papi R, Pantazaki A, Kyriakidis D, Cordopatis P, Manessi-Zoupa E. J Inorg Biochem. 2008 Jul;102(7):1397-405. doi: 10.1016/j.jinorgbio.2008.01.001. Epub 2008 Jan 8.
Two new organotin(IV) complexes with dianionic dipeptides containing the alpha-aminoisobutyryl residue (Aib) as ligands are described. The solid complexes [(n-Bu)(2)Sn(H(-1)L(A))] x 2MeOH (1 x 2MeOH) (L(A)H=H-Aib-L-Leu-OH) and [(n-Bu)(2)Sn(H(-1)L(B))] x MeOH (2 x MeOH) (L(B)H=H-Aib-L-Ala-OH) have been isolated and characterized by single-crystal X-ray crystallography and spectroscopic techniques (H(-1)L(2-) is the dianionic form of the corresponding dipeptide). Complexes 1 x 2MeOH and 2 x MeOH are monomeric with similar molecular structures. The doubly deprotonated dipeptide behaves as a N(amino), N(peptide), O(carboxylate) ligand and binds to the Sn(IV) atom. The five-coordinate metal ion has a distorted trigonal bipyramidal geometry. A different network of intermolecular hydrogen bonds in each compound results in very dissimilar supramolecular features. The IR, far-IR, Raman and (119)Sn NMR data are discussed in terms of the nature of bonding and known structures.
2.Chain length effects on helix-hairpin distribution in short peptides with Aib-DAla and Aib-Aib segments.
Rajagopal A1, Aravinda S, Raghothama S, Shamala N, Balaram P. Biopolymers. 2011;96(6):744-56. doi: 10.1002/bip.21613. Epub 2011 Mar 7.
The Aib-D Ala dipeptide segment has a tendency to form both type-I'/III' and type-I/III β-turns. The occurrence of prime turns facilitates the formation of β-hairpin conformations, while type-I/III turns can nucleate helix formation. The octapeptide Boc-Leu-Phe-Val-Aib-DAla-Leu-Phe-Val-OMe (1) has been previously shown to form a β-hairpin in the crystalline state and in solution. The effects of sequence truncation have been examined using the model peptides Boc-Phe-Val-Aib-Xxx-Leu-Phe-NHMe (2, 6), Boc-Val-Aib-Xxx-Leu-NHMe (3, 7), and Boc-Aib-Xxx-NHMe (4, 8), where Xxx=DAla, Aib. For peptides with central Aib-Aib segments, Boc-Phe-Val-Aib-Aib-Leu-Phe-NHMe (6), Boc-Val-Aib-Aib-Leu-NHMe (7), and Boc-Aib-Aib-NHMe (8) helical conformations have been established by NMR studies in both hydrogen bonding (CD3OH) and non-hydrogen bonding (CDCl3) solvents. In contrast, the corresponding hexapeptide Boc-Phe-Val-Aib-DAla-Leu-Phe-Val-NHMe (2) favors helical conformations in CDCl3 and β-hairpin conformations in CD3 OH.
3.Crystal-state 3D-structural characterization of novel, Aib-based, turn and helical peptides.
Crisma M1, Andreetto E, De Zotti M, Moretto A, Peggion C, Formaggio F, Toniolo C. J Pept Sci. 2007 Mar;13(3):190-205.
The crystal-state conformations of the hexapeptide amide Pht-(Aib)(6)-NH-C(CH(3))(2)-O-OtBu (7), the hexapeptide Ac-L-aIle-(Aib)(5)-OtBu (6), the pentapeptide Z-(Aib)(3)-L-Glu(OtBu)-Aib-O-(CH(2))(2)-(1)Nap (5), the tetrapeptides Z-(Aib)(2)-L-His(N(tau)-Trt)-Aib-OMe (4 I) and Z-(Aib)(2)-L-Nva-Aib-OtBu (4 II), the tripeptide Pyr-(Aib)(3)-OtBu (3 I), the dipeptide amides Pyr-(Aib)(2)-(4)NH-TEMPO (3 II) and Piv-(Aib)(2)-NH-C(CH(3))(2)-O-OtBu (3 III), and the dipeptides Pht-Aib-betaAc(6)c-OtBu (2 I), Pht-Aib-NH-C(CH(3))(2)-O-OtBu (2 II) and Boc-gGly-mAib-OH (2 III) have been determined by X-ray diffraction analyses. All peptides investigated are characterized by one or more turn/helix forming Aib residues. Except the three short dipeptides, all are folded into C==O...H--N intramolecularly H-bonded 3(10)-helices, or into various types of beta-turns. In the structure of 6, two independent molecules of opposite screw sense were observed in the asymmetric unit, generating diastereomeric 3(10)-helices.
