Cyclopenine degradation

Table II compiles melting points, optical rotations, and methods used for the structural elucidation of the known benzodiazepine alkaloids. Intensive studies of the degradation of the molecules as well as attempts at total synthesis have been undertaken only with members of the cyclopenin and the anthramycin-tomaymycin groups. In the following a short summary is given of the reactions and intermediates that provided essential information about the structures of the basic skeletons of the alkaloids.

Fig. 2. Degradation of cyclopenin and cyclopenol (45,51). Degradation products are numbered in relation to the parent alkaloids. 

These data, taken together with mass spectrometric degradation and other spectral evidence (see Table II), clearly favor a seven-membered cyclic peptide formed from anthranilate and phenylalanine as the basic skeleton of cyclopenin (3) and cyclopenol (4). This structure, including the epoxide linkage, was further supported by biosynthetic probing (51,52) (see Section IV,A). 

The benzodiazepine alkaloids cyclopenin and cyclopenol were isolated by Bracken et al. and Birkinshaw et al. from the culture medium of Penicillium cyclopium [191, 192]. The structures of these alkaloids 188 and 189 were elucidated on the basis of oxidative degradation (Figure 3.61) [193]. 

---