Cyclopeptides fragmentation

Cyclopeptides and peptides with N-heterocyclic fragments as pep-tidomimetics 93AG(E)1244. 

In den Massenspektren der Cyclopeptide lassen sich einige Zerfalls-reaktionen nachweisen, die charakteristisch fiir bestimmte Aminosaure-Reste sind. So eliminieren Cyclopeptide des Leucins die Leucinseiten-kette durch eine McLafferty-Umlagerang als Isobuten aus Molekul- und Fragment-Ionen. Die Benzyl-Seitenkette eines Phenylalaninrestcs kann, wie bei den Dioxopiperazinen, als Radikal aus dem Molekiil-Ion abge-spalten werden. Im Massenspektrum des Cyclo-(gly-ala-phe-gly-ala-phe) liefert diese Reaktion die Ionen MZ 459. 

Comparison of fragments lost from cyclopeptides a and b observed in the FD/B/fi/CAD spectra [223]... 

The major fragmentations are represented in Figure 81 for both a and b cyclopeptides. 

Zhao M, Lin N, Wang C, et al. (2003). Synthesis and thrombolytic activity of fibrinogen fragment related cyclopeptides. Bioorg. Med. Chem. Lett. 9 961-964. 

The main tools for structure elucidation nowadays are MS and NMR spectroscopy. MS is extensively used as an important tool for identification. Besides determining the molecular weight, it provides substantial information about the structure of the alkaloids since the various groups of cyclopeptide alkaloids fragment in a predicted and well described way. In recent years use of high field NMR spectroscopy has made structure elucidation of the cyclopeptide alkaloids considerably easier. 

Fragmentation of 4(14)-Frangulanine- and -Integerrine-lype Cyclopeptide Alkaloids... 

The main fragments of these 4(14) cyclopeptide alkaloids are shown below in Fig. 2 miz values of ions are in parentheses). 

Fig. 2. Main fragments of 4(14)-frangulanine- and -integerrine-type cyclopeptide alkaloids...

Fragments t-v not only reveal the nature of unit D of the cyclopeptide alkaloid (aminophenol moiety) but confirm the identity of R (t,u) and... 

Common fragments are fragments that give no information about R, R R R and R but confirm the nature of the aminophenol moiety. Furthermore their occurrence is indicative of 4(14) cyclopeptide alkaloids. Fragment u and common fragments with mh 120, 107 and 103 are more frequent for the 4(14)-pandamine types. 

Ceanothines B, C and D which belong to the category of 4(14)-frangulanine-type cyclopeptide alkaloids, bear NMePro as basic terminal amino acid. In this case a = a (m/z = 84), while fragments b, n, o and p are absent. 

Mass spectra of 4(14)-Pandamine-type cyclopeptide alkaloids contain all the fragments previously described and in addition fragments b", f and i (Fig. 5, Table 6). These last fragments are related to... 

Fig. 5. Special fragments of 4(14)-pandamine-type alkaloids Table 6. m/z Fragments of 4(14)-Pandamine-Type Cyclopeptide Alkaloids...

Fragmentation of 5(13)-Zizyphine-A-iype and 5(14)-Amphibine-B-Type Cyclopeptide Alkaloids... 

Fig. 9. Fragments r-u of 5(13)-zizyphine-A-type and 5(14)-amphibine-B-type cyclopeptide alkaloids...

Fragmentation of 5(14)-Scutianine-A-iype Cyclopeptide Alkaloids (Hymenocardine included)... 

The main fragmentation pattern of this category follows that of the 4(14)-frangulanine-, -integerrine- and -pandamine-type cyclopeptide alkaloids and exhibits the same a-m and q-v fragments. 

Fragments c and d have slightly modified structures due to the existence of Pro as additional amino acid. For the same reason the MS of all of these compounds contains fragment q which, in the case of hymenocardine, corresponds to q" of 5(13)-zizyphine-A and 5(14)-amphibine-B cyclopeptide alkaloids. 

Because all 5(14)-scutianine-A type cyclopeptide alkaloids contain Phe as the basic terminal amino acid, fragments homologous to n, o and p of 4(14)-cyclopeptide alkaloids are absent. Fragments w, x, y, z, c and d are group specific, while c and d arise from the same fragmentation pattern giving c and d of 5(14)-amphibine-type cyclopeptide alkaloids (Fig. 13). 

Fig. 13. Fragmentation of 5(14)-scutianine-A-type cyclopeptide alkaloids References, pp. 171-179...

Fragments a, b, d, g, j, q, r, v, w and x of hymenocardine follow the fragmentation pattern of 5(14)-scutianine-A-type cyclopeptide alkaloids. Due to the existence of lie as the basic terminal amino acid it gives fragments n and o of 4(14)-cyclopeptide alkaloids. Furthermore two special fragments, namely i and i, occur (Fig. 14). 

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