A new cyclic peptide, ascidiacyclamide, isolated from ascidian

Abstract

A n e w cytotoxic cyclic peptide, ascidiacyclamide, has been isolated from ascidian and its structure has been elucidated by n.m.r. spectroscopy.

Formation of mononuclear and chloro-bridged binuclear copper(II) complexes of patellamide D, a naturally occurring cyclic peptide: influence of anion and solvent

“…Our interest has been in the coordination chemistry of cyclic peptides having a 24-azacrown-8-macrocyclic structure (Chart 1); these compounds have been isolated and purified from the aplousobranch ascidian Lissoclinum patella [18][19][20][21]. X-ray crystal structures of ascidiacyclamide (1) and patellamide D (2) (Chart 1) reveal two different conformations of these cyclic peptides [22][23][24][25].…”

Cyclic peptide marine metabolites and CuII

“…NMR studies have shown that the pseudo-octapeptides adopt identical conformations in solution and the solid state. 26,33,36,66,72,86 In the "saddle-shaped" conformation all nitrogen atoms point towards the inside of the macrocycle, while the "figure-ofeight" conformation is characterized by intramolecular H-bonds, N-H⋯OvC and N-H⋯O oxa (oxazoline ring), that lead to a rotation of the oxazoline rings such that the N oxa atoms face the outside of the macrocycle. 27 Several reasons for the different preferences are discussed in the literature.…”

“…A substantial increase in flexibility compared to the cyclic pseudo-hexa-and pseudo-heptapeptides might be expected. However, analysis of the solid state and solution structures by X-ray crystallography, 27,73,74,84,85 1 H-NMR spectroscopy, 19,33,72,85 DFT calculations 74 and molecular mechanics/ Monte Carlo/molecular dynamics-based conformational analyses 27,72 indicated that there are four conformers which we summarize here in two types of conformations: the "saddleshaped", sometimes also referred to as square, and the twisted "figure-of-eight" conformation (Fig. 4).…”

“…[22][23][24] Oxazoline-, thiazole-, and thiazoline-based cyclic pseudo-hepta-and pseudo-octapeptides, e.g. lissoclinamides, [25][26][27][28][29] patellamides, [30][31][32] and ascidiacyclamide 33,34 can be extracted from L. patella; L. bistratum on the other hand provides oxazoline-based cyclic pseudo-hexapeptides such as westiellamide 35,36 and bistratamide A-H (Scheme 1). 17,[37][38][39][40] In the cyclic peptides, heterocyclic moieties alternate with D-and L-amino acid residues in the peptide sequence.…”

Syntheses and Structures of Imidazole Analogues of Lissoclinum Cyclopeptides

“…[3] The Lissoclinum class of cyclic peptides, such as westiellamide (1) [4] or ascidiacyclamide (2), [5] belongs to these alkaloids and is characterized by an alternating sequence of oxazole, thiazole, oxazoline, and thiazoline moieties with hydrophobic standard amino acid residues. [6] These five-membered heterocyclic rings result from condensation of serine, threonine, and cysteine side chains with the preceding carbonyl groups in a peptide sequence.…”