Cyclic peptides, from plants, isolation

H. Other Isolations of Cyclic Peptides from Plants. 371... 

Cyclic peptides have been isolated from various plant spieces, and these alkaloids are now considered to be a rather popular class of metabolites. Alkaloids reported by other groups are listed as follows ... 

Antitumor compounds, among them cyclic peptides, terpenoids, and alkaloids isolated from higher plants 99YZ529. 

Some of the medicinal plants belonging to the Caryophyllaceae family contain cyclic peptides. This is rare in higher plants. ITie roots of Stellaria dichotoma L. var. lanceolata Bge. have been used in folk medicine as an antifebrile agent. A series of dichotomins, cyclic penta- and hexapeptides, have been isolated from the roots of S. dichotoma L. var. lanceolata, and the structures of dichotomins A-E (331-335), as shown in Fig. 47, were established on the basis of extensive 2D-NMR, chemical degradation, and X-ray crystallographic analysis 236,237). Liu et al. also reported the structure of a cyclic hexapeptide, named stellaria cyclopeptide, cyc/o(-Gly-Gly-Ala-Ala-Val-Tyr-), isolated from the same plant 238). 

The final chapter, by Itokawa, Takeya, Hitotsuyanagi, and Morita, reviews the various macrocyclic peptide alkaloids isolated from plants. In addition to a general overview of the many new peptide and amide alkaloids that have been isolated recently from a diverse range of plant families, this review places particular emphasis on the structure-activity relationships, the conformational analysis, and the antitumor activity of the RA series of cyclic oligopeptides from Rubia spp. 

Dianthins, cytotoxic cyclic peptides isolated from the methanol extract of the traditional Chinese medical plant Dianthus superbus. Beside dianthin C, cyclo-(-Gly-Pro-Phe-Tyr-Val-Ile ), the dianthins D-F with similar... 

A special type of deterrent effect was shown by Ma (1977b). A sesquiterpene dialdehyde isolated from the warburgia plant blocks the sugar receptor cell of S. exempta for 10-20 min after two contacts of 3 min. This inhibitory effect on the sensory neuron has been correlated with a suppression of the feeding response to sucrose. Similarly, Kennedy and Halpern (1980) showed that ziziphin, a cyclic peptide alkaloid of Rhamnaceae, also temporarily inhibits the fly sugar (but not the salt) receptor. 

DKPs are simple and easy to obtain and are quite common by-products of synthetic, spontaneous, and biological formation pathways. DKP formation has been well documented as side reactions of solid-phase and solution-phase peptide synthesis. In addition, DKPs have been shown to be decomposition products of various peptides, proteins, and other commercial pharmaceuticals. Cyclic dipeptides were found to be present in solutions of human growth hormone, bradykinin, histerlin, and solutions of agents within the classes of penicillins and cephalosporins. " DKPs are also enzymatically synthesized in several protists and in members of the plant kingdom. Hydrolysates of proteins and polypeptides often contain these compounds and they are commonly isolated from yeasts, lichens, and fungi. ... 

Furthermore, an acyclic astin J (307) has been isolated (186). Cheng et al. reported this kind of acyclic peptide, the asterinins A-C, from the same plant (187). Base-catal) zed cleavage of astins A, B, and C with a fi,y-dichlorinated proline resulted in acyclic peptides with pyrrole rings, which were considered to be produced by dechlorination and aromatization from Pro(Cl2) to pyrrole imder basic conditions, following the cleavage of the amide bond in Pro. The acyclic astin B was also produced from the cyclic astin B by hepatic microsomal biotransformation in rats (Fig. 36) (188). 

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