Viomycin. I. The Structure of Viomycidine

Metabolic solutions to the biosynthesis of some diaminomonocarboxylic acids in nature: Formation in cyanobacteria of the neurotoxins 3-N-methyl-2,3-diaminopropanoic acid (BMAA) and 2,4-diaminobutanoic acid (2,4-DAB)

The non-encoded diaminomonocarboxylic acids, 3-N-methyl-2,3-diaminopropanoic acid (syn: α-amino-β-methylaminopropionic acid, MeDAP; β-N-methylaminoalanine, BMAA) and 2,4-diaminobutanoic acid (2,4-DAB), are distributed widely in cyanobacterial species in free and bound forms. Both amino acids are neurotoxic in whole animal and cell-based bioassays. The biosynthetic pathway to 2,4-DAB is well documented in bacteria and in one higher plant species, but has not been confirmed in cyanobacteria. The biosynthetic pathway to BMAA is unknown. This review considers possible metabolic routes, by analogy with reactions used in other species, by which these amino acids might be biosynthesised by cyanobacteria, which are a widespread potential environmental source of these neurotoxins. Where possible, the gene expression that might be implicated in these biosyntheses is discussed.

Total Syntheses of (+/-)-Deethylibophyllidine Using a Crisscross Annulation: Ring Cleavage of Octahydroindolo[2,3-a]quinolizines Followed by Tandem Cyclizations of Octahydroazecino[5,4-b]indoles

The total synthesis of (+/-)-deethylibophyllidine (1) is described. Three different sequences provide this pentacyclic alkaloid using a common strategy involving a crisscross annulation. Key steps include (i) C/D ring cleavage of a 2-formyloctahydroindolo[2,3-a]quinolizine to obtain octahydroazecino[5,4-b]indoles, via either a chloroformate induced process or a quaternary ammonium salt formation followed by treatment with lithium, and (ii) a tandem process consisting of an intramolecular Pictet-Spengler double cyclization upon a beta-indole position of a 2,3-disubstituted indole to generate the quaternary spiro center of the pentacyclic skeleton of ibophyllidine alkaloids. Attempts to extend the procedure to the construction of the pentacyclic framework of (+/-)-ibophyllidine result in very low yield.