title: Solvent-Directed Switch of a Left-Handed 10/12-Helix into a Right-Handed 12/10-Helix in Mixed β-Peptides.
abstract: Present study describes the synthesis and conformational analysis of β-peptides from C-linked carbo-β-amino acids [β-Caa(l)] with a d-lyxo furanoside side chain and β-hGly in 1:1 alternation. NMR and CD investigations on peptides with an (S)-β-Caa(l)monomer at the N-terminus revealed a right-handed 10/12-mixed helix. An unprecedented solvent-directed "switch" both in helical pattern and handedness was observed when the sequence begins with a β-hGly residue instead of a (S)-β-Caa(l)constituent. NMR studies on these peptides in chloroform indicated a left-handed 10/12-helix, while the CD spectrum in methanol inferred a right-handed secondary structure. The NMR data for these peptides in CD3OH showed the presence of a right-handed 12/10-helix. NMR investigations in acetonitrile indicated the coexistence of both helix types. Quantum chemical studies predicted a small energy difference of 0.3 kcal/mol between the two helix types, which may explain the possibility of solvent influence. Examples for a solvent-directed switch of both the H-bonding pattern and the handedness of foldamer helices are rare so far. A comparable solvent effect was not found in the corresponding peptides with (R)-β-Caa(l)residues, where right-handed 12/10-helices are predominating.
authors.affiliation: Organic and Biomolecular Chemistry Division, CSIR-Indian Institute of Chemical Technology , Hyderabad 500 007, India.
authors.forename: Prashanth
authors.initials: P
authors.lastname: Thodupunuri
authors.affiliation: Nuclear Magnetic Resonance & Structural Chemistry Division, CSIR-Indian Institute of Chemical Technology , Hyderabad 500 007, India.
authors.forename: Sirisha
authors.identifier: 0000-0002-4951-8092
authors.initials: S
authors.lastname: Katukuri
authors.affiliation: Nuclear Magnetic Resonance & Structural Chemistry Division, CSIR-Indian Institute of Chemical Technology , Hyderabad 500 007, India.
authors.forename: Kallaganti V S
authors.initials: KV
authors.lastname: Ramakrishna
authors.affiliation: Organic and Biomolecular Chemistry Division, CSIR-Indian Institute of Chemical Technology , Hyderabad 500 007, India.
authors.forename: Gangavaram V M
authors.identifier: 0000-0001-5638-788X
authors.initials: GV
authors.lastname: Sharma
authors.affiliation: Nuclear Magnetic Resonance & Structural Chemistry Division, CSIR-Indian Institute of Chemical Technology , Hyderabad 500 007, India.
authors.forename: Ajit C
authors.initials: AC
authors.lastname: Kunwar
authors.affiliation: Nuclear Magnetic Resonance & Structural Chemistry Division, CSIR-Indian Institute of Chemical Technology , Hyderabad 500 007, India.
authors.forename: Akella V S
authors.initials: AV
authors.lastname: Sarma
authors.affiliation: Institute of Biochemistry, Faculty of Biosciences, University of Leipzig , Brüderstrasse 34, D-04103 Leipzig, Germany.
authors.forename: Hans-Jörg
authors.initials: HJ
authors.lastname: Hofmann