Visita University Chemical Laboratory, Cambridge (UK) 1985/86

Studi sulla biosintesi della vitamina B12: sintesi chimica degli ipotetici precursori biosintetici marcati con isotopi (radioattivi o stabili) ed esperimenti della loro incorporazione enzimatica nell'acido cobirinico. Caratterizzazione del prodotto della prima C-metilazione dell'uroporfirinogeno III, precorrina I. Sintesi e cristallizzazione dell'eptametil-estere dell'acido diciano 15'- norcobirinicos

Visita University Chemical Laboratory . Cambridge (UK) 1984/85

Studi sulla biosintesi della vitamina B12: sintesi chimica degli ipotetici precursori con marcatura isotopica ed esperimenti della loro incorporazione enzimatica nell'acido cobirinico. Ruolo degli acidi 5'- e 15'-norcobirinici.s

Visita University Chemical Laboratory, Cambrigde (UK), 1987

Studi sulla vitamina B12: Sintesi e cristallizzazione dell'eptametilestere dell'acido diciano 15'-norcobirinic

Studies on the biosynthesis of syringomycin E and syringopeptin 22A

Feeding radioactive putative precursors to the bacterial cultures of Pseudomonas syingae pv. syringae in the presence of a protein synthesis inhibitor allowed the formation of radiolabelled syringomycin and syringopeptin. The result indicates that a nonribosomal mechanism of peptide synthesis is operating in the formation of these peptide metabolites

Bioactive lipopeptides of Pseudomonas syringae

Structural features and biological activities of lipodepsipeptides produced by various strains of the widely spread phytopathogenic bacterium Pseudomonas syringae pv. syringae ae presented here. Emphasis is put on biotechnological and potential biomedical applications of this family of secondary metabolites. In this context, structurally related metabolites from other Pseudomonas species are also considered

Reaction of 3-halomethyl-2-cephem derivatives with phenols

2-cephem allylic bromides are important, versatile intermediates for the derivatization of C-3’ position in cephalosporines. We showed that they can react smoothly with phenols, yielding the C-3’ cephem derivatives by C-alkylation of phenols

Biosynthesis of bioactive lipodepsipeptides by Pseudomonas syringae pv. syringae.

The biosynthesis of the lipodepsipeptides syringomycin and syringopeptin 22, secondary metabolites produced by the strain B301D-R of the phytopathogenic bacterium Pseudomonas syringae pv. syringae, was investigated by feeding radioactively labeled precursors to chloramphenicol-contg. bacterial suspensions. The prodn. of labeled metabolites in the presence of a protein biosynthesis inhibitor showed that a nonribosomal mechanism is operating in their synthesis. The origin of the modified amino acidic residues was studied by comparing the specific activities of the intact lipodepsipeptides, derived from the feedings of L-[14C(U)]-Thr or L-[14C(U)]-Asp, to those of the constituent amino acids, obtained by hydrolytic degrdn. of the peptides, followed by appropriate derivatizations and isolation of the single structural elements by RP-HPLC. The results show that L-threonine is the precursor of dehydrobutyrin in syringomycin and in syringopeptin 22 and of 4-chlorothreonine in syringomycin. These two residues are also labeled by aspartic acid, which is the biosynthetic precursor of threonine. Moreover, aspartic acid is also incorporated into 2,4-diaminobutyric and 3-hydroxyaspartic acid in syringomycin

Evidence of the non ribosomal biosynthetic mechanism in the formation of syringomycin and syringopeptin, bioative lipodepsipeptides of the phytopathogenic bacterium Pseudomonas syringae pv. syringae

Syringomycin and syringopeptins are lipodepsipeptide metabolites produced by the phytopathogenic bacterium Pseudomonas syringae pv. syringae. Radioactively labelled lipopeptides were produced in whole cell cultures supplemented with radioactively labelled putative biosynthetic precursors in the presence of the protein synthesis inhibitor, chloramphenicol. The results indicate that these lipopeptides are formed by a nonribosomal mechanism of peptide synthesis

The substrate specificity of the syringomycin synthetase adenylation domains

The megasynthetase SyrE in the syringomycin biosynthesis multienzyme complex comprises eight adenylation domains. the substrate specificity and stereospecificity of these domains was investigated

Substrate specificity of syringomycin synthetase adenylation domains.

The three-dimensional structures of the adenylation domains (A) of eight modules of SyrE, a peptide synthetase involved in the biosynthesis of syringomycin, was investigated by homology modeling using as a template the adenylation domain of gramicidin synthetase 1. Multiple sequence alignment of the adenylation domains of each of the eight modules of SyrE, allowed to identify the residues which delimitate the active site pockets. The active sites of the A domains of SyrE1 and SyrE2, involved in the insertion of the two serine residues in syringomycin, are essentially equivalent. The docking of these models with L-Ser and D-Ser showed that L-Ser is preferred as a substrate on the basis of stabilizing interactions. This is in accordance with previously shown stereo-specificity of these modules. Analogous investigation carried out on the modules SyrE3 and SyrE4 showed the preference for the L-isomer of their substrate, 2,4-diaminobutyric acid. In addition, the model of SyrE8, whose substrate amino acid is arginine, allowed to evidence specificity - conferring residues for this residue, which had not been previously reported