Lunaria biennis Lunarine

The combination of spermidine, as the basic component, and two cinnamic acid units to form an amide is realized in some alkaloids isolated from Lunaria biennis. Structure 91 was determined by X-ray crystallography for the main alkaloid lunarine (84-86). 

Another satellite alkaloid of Lunaria biennis is numismine (100). Its structure was deduced by comparing its tetrahydro derivative to hexahydro-lunarine and finding both products to be identical (see Section V). 

Lunarine (26), a constituent of Lunaria biennis M., is a member of neolignans (see Scheme 4). Biomimetic synthesis of tetrahydrolunarine (720) was performed by K3Fe(CN)e-promoted oxidation of methyl p-hydroxyphenylpropionate (721) as a key step. 721 was oxidized with K3Fe(CN)e in aq. Na2C03 (0 °C, 3.5 h) to give in 14% yield an ortho-para coupled product 722, which was further converted to the target molecule 720 (Scheme 142) . ... 

The absolute stereochemistry of the spermidine-based alkaloid lunarine, isolated from Lunaria biennis, has been determined by two groups on two different heavy-atom salts.28,29 The final representation (35) is the reverse of that arbitrarily selected and jointly published by these workers in preliminary form. 

Lunarine.— The biosynthesis of lunarine (109) has been studied in Lunaria biennis. Although [3 - C]phenylalanine was incorporated, [3 - C]tyrosine was not Consequently, phenylalanine is converted first into cinnamic acid, which is then hydroxylated. Oxidative coupling of p-hydroxycinnamic acid and cyclization would give (110), the analogue of Pummerer s ketone, and thence to... 

Alkaloids based on these structural units are widespread, but sporadically distributed, in nature at least 125 alkaloids of this type are known (Verpoorte et al., 1991). The first reported was lunarine (18), from Lunaria biennis (Brassica-ceae), which was reported in 1908, although the correct structure was established only in 1965 (Fig. 28.12). Palus-trine (19), from Equisetum palustre (Equisetaceae), also was reported quite early (Badwani et al., 1973). 

---