β‐Helical structures of Boc‐(L‐Val‐D‐Val)₆‐OMe in the crystalline state and in chloroform

Abstract

SummaryA conformational study was carried out on Boc-(~-Val-~-Val)~-OMe in the crystalline state by X-ray and IR. and by 'H-NMR. in chloroform. The dodecapeptide crystallizes from CHCl,/EtOAc with a left-handed helical structure of the type TL /?5.6, and from CHCI3/MeOH (or MeOH) with a different structure. In chloroform it forms three slowly interconverting species: one is a ?J p5.6 left-handed helical species, and the other two are most likely single-stranded p4.4 helical species of opposite handedness. The double-stranded helical species is. predominant in fresh solutions of samples obtained from CHCI,/EtOAc. Because of the slow conversion or formation of this species some hours are needed to reach the conformational equilibrium in chloroform at 25 ' .

Sequestration of connexin43 in the early endosomes: An early event of Leydig cell tumor progression

“…Später konnte man durch NMR‐Untersuchungen das Vorliegen ähnlicher linksgängiger doppelhelicaler Strukturen in Lösung belegen 45–47. Bei verwandten höheren Homologen fand man, dass sie überwiegend als Mischungen aus monomeren links‐ und rechtsgängigen β 4.4 ‐Helices vorlagen, vermutlich wegen einer im Vergleich zum Octapeptid besseren Möglichkeit zur Bildung intramolekularer H‐Brücken 48–50. Lorenzi beobachtete ebenfalls eine Gramicidin‐artige Kopf‐Kopf‐Dimerisierung von monomeren β 4.4 ‐Helices aus dem N‐formylierten Nonapeptid HCO‐ L ‐Ile‐( D ‐aIle‐ L ‐Ile) 4 ‐OMe51 (aIle=Alloisoleucin) und beim Heptapeptid HCO‐ L ‐Phe‐( D ‐Phe‐ L ‐Phe) 4 ‐OMe die Bildung eines Tetramers, bei dem es sich um ein ungewöhnliches Kopf‐Kopf‐Dimer aus doppelsträngigen ↑↑ β 5.6 ‐Helices handelt 52…”

.beta.-Helical structure of D,L-alternating oligophenylalanines with terminal butyloxycarbonyl and methoxy groups in chloroform: comparison with oligovalines

“…In the case of VI1 we have determined the type of relative arrangement of the chains by using 'H NMR spin-lattice re1axati0n.I~ As Figure 3 schematically shows, the protons 'H"(1) and 'H" (5) are near to each other in the tl@5.6-helix A and far apart in the tt@5.6-helix C. The observation (Table 111) that the 'H"(5) has a significantly higher Tl value in the deuterated analogue 2Ha(1)-VII than in VI1 demonstrates that the two a-protons are proximate, and hence that for VI1 the antiparallel structure A is the correct one. In the case of VI1 we have determined the type of relative arrangement of the chains by using 'H NMR spin-lattice re1axati0n.I~ As Figure 3 schematically shows, the protons 'H"(1) and 'H" (5) are near to each other in the tl@5.6-helix A and far apart in the tt@5.6-helix C. The observation (Table 111) that the 'H"(5) has a significantly higher Tl value in the deuterated analogue 2Ha(1)-VII than in VI1 demonstrates that the two a-protons are proximate, and hence that for VI1 the antiparallel structure A is the correct one.…”

Peptides with regularly alternating enantiomeric sequence: From ion channel models to bioinspired nanotechnological applications

“…The roles that various structural factors can have in the conformations of l , d ‐peptides, such as the length of the chain, the nature of the side chains, and the specific configuration motif ( dld or ldl ), were investigated. To this end, l , d ‐α‐peptides with different sequences and lengths were synthesized and their conformational properties were investigated …”

“…Single crystal X‐ray diffraction analysis and spectroscopic results in solution established that the octamer Boc‐( l ‐Val‐ d ‐Val) 4 ‐OCH 3 was prevalently in antiparallel double‐stranded β‐helix conformation closely related to the X‐ray crystal structure of gramicidin A . However, structural investigations on Boc‐( l ‐Val‐ d ‐Val) 6 ‐OCH 3 and Boc‐( l ‐Val‐ d ‐Val) 8 ‐OCH 3 revealed that single‐stranded β‐helices are stable conformations for longer sequences.…”