Dario Ghiringhelli

The biosynthesis of aureothin

Abstract Feeding experiments with specifically labelled precursors show that the nitroaromatic, C-6-C-1 unit of the antibiotic aureothin (9) biologically derives by degradation of the C-6-C-3, phenylpropanoid precursor D,L -p-aminophenylalanine (1) through hydroxylation β to the nitrogen to erythro and threo p-aminophenylserine (3 and 4). During the biosynthesis there is the loss of the hydrogen originally present in benzylic position in the phenylpropanoid precursor, and, further, the oxidation of the p-amino group to p-nitro takes place very late in the sequence.

Formation of the (R)- and (S)-enantiomers of ethyl 3-hydroxybutanoate and of 1-(1,3-dithian-2-yl)-2-hydroxypropane by microbial reduction

The (R)and (S) enantiomers of 3-hydroxybutanoate [(2a) or (3a)] and 1-(1,3-dithian-2-yl)-2-hydroxypropane [(2b) or (3b)] are obtained from ethyl 3-oxobutanoate (1a) and 1-(1,3-dithian-2-yl)-2-oxopropane (1b), respectively, using growing cultures from different strains of Geotrichum candidum and Aspergillus niger.

Structure determination of two extractives from Aspergillus amstelodami by nuclear magnetic resonance spectroscopy

Spectral evidence supports the assignment of structures (1) and (2) to two substances extracted from the mycelium of Aspergillus amstelodami; they can be obtained by thermal condensation of auroglaucine with neoechinuline B and neoechinuline C, respectively, which are all known metabolites of the fungus.

Stereochemical course of the enzymic synthesis of L-tyrosine from phenol and L-serine catalysed by tyrosine phenol lyase from Escherichia intermedia

The enzymic synthesis of L-tyrosine from phenol and L-serine catalysed by fibre-entrapped tyrosine phenol lyase from Escherichia intermedia proceeds with retention of configuration.

On the synthesis of serine and homoserine samples asymmetrically labelled with tritium and deuterium in the hydroxymethylene group.

(1 R) [1-3H,2H1] 3-Phenylpropanol, the key intermediate in the synthesis of (4 R) [4-3H,2H1] D, L-homoserine and of the (4 S)-isomer, is obtained from (1 S) [1-2H1] 3-phenylpropanol and (1 RS) [1-3H] ethanol upon incubation with yeast alcohol dehydrogenase and NAD+; under similar conditions 2-phenylethanol undergoes very small exchange with [1-2H2] ethanol.

Pattern of incorporation of leucine samples asymmetrically labelled with 13C in the isopropyl unit into the C5-isoprenoid units of echinuline and flavoglaucine

The labelling pattern of the C5-isoprenoid moieties of echinuline (18) and flavoglaucine (19) obtained in feeding experiments of Aspergillus amstelodami of 90% enriched (4R)[5-13C]leucine (11) and of the (4S)-isomer (12), determined by 13C-n.m.r. spectroscopy, appears in agreement with a preferential incorporation of the carbon atom of the pro-S methyl group of the stereospecifically labelled amino acid (12) into the C-3 methyl group of the intermediate mevalonic acid and of the carbon atom of the pro-R methyl group of (11) in position 4, respectively.

Synthesis of homoserine samples stereospecifically labelled with isotopic hydrogen in the β- and γ-positions

(βR)[β-2H]-L-Homoserine (17) and the (βS)-isomer (8) are synthesised through a sequence involving as key step the formal cis addition of hydroxylamine onto cinnamic acid to form 3-amino-3-phenylpropionic acid; (γR)[γ-2H]-DL-homoserine (20) and the (γS)-isomer (19) are obtained from the enantiomeric forms of stereospecifically labelled 3-phenyl[1-2H]propanol.

Biosynthesis of narcissidine

Feeding experiments show that the conversion of O-methylnorbelladine (1) into narcissidine (8) involves the loss of a pro-S hydrogen from C-4 ofgalanthine (4)

Anaesthetic properties of some esters of 2-piperidylcarbinols

Vengono brevemente discussi i rapporti fra struttura e attività anestetica di un gruppo di difenilacetati di amino alcoli ciclici riportati nella tabella.

Synthesis of the two enantiomers of 1-chloro-1,1-difluoro-3-(p-tolylsulphonyl)propan-2-ol by microbial reduction of the parent propanone and transformation into 3,3-difluorotetrahydrofuran derivatives

Both R and S enantiomers of 1-chloro-1,1-difluoro-3-(p-tolylsulphonyl)propan-2-ol were obtained with high enantioselection by microbial reduction of 1-chloro-1,1-difluoro-3-(p-tolylsulphonyl)propan-2-one. The enantiomerically pure R-alcohol was obtained and transformed into 3,3-difluoro-4-methyl-2-[(p-tolylsulphonyl)methyl]tetrahydrofurans through a two-step synthesis.