Cristina Forzato

Microbial bioreductions of γ- and δ-ketoacids and their esters

Abstract A series of yeasts were used in the bioreductions of aliphatic and aromatic γ- and δ-ketoacids and esters to investigate the preparation of enantiomerically pure γ- and δ-lactones through the intermediacy of their corresponding γ- and δ-hydroxyacids and esters. Bioreduction of ethyl 4-oxononanoate 2a with Pichia etchellsii afforded the γ-nonanolide (+)- 5a with 99% e.e., while Pichia minuta proved to be the best choice for the bioreduction of ethyl 2-oxocyclohexylacetate 2e , which afforded cis -(−)- 5e and trans -(−)- 5e with 98 and 99% e.e., respectively. Reduction of 3-(2-oxocyclohexyl)propionic acid 3e with Pichia glucozyma gave predominantly the corresponding δ-lactone trans -(−)- 6e with 94% e.e., whose absolute configuration was determined by means of CD spectroscopy.

Interaction of chlorogenic acids and quinides from coffee with human serum albumin.

Chlorogenic acids and their derivatives are abundant in coffee and their composition changes between coffee species. Human serum albumin (HSA) interacts with this family of compounds with high affinity. We have studied by fluorescence spectroscopy the specific binding of HSA with eight compounds that belong to the coffee polyphenols family, four acids (caffeic acid, ferulic acid, 5-O-caffeoyl quinic acid, and 3,4-dimethoxycinnamic acid) and four lactones (3,4-O-dicaffeoyl-1,5-γ-quinide, 3-O-[3,4-(dimethoxy)cinnamoyl]-1,5-γ-quinide, 3,4-O-bis[3,4-(dimethoxy)cinnamoyl]-1,5-γ-quinide, and 1,3,4-O-tris[3,4-(dimethoxy)cinnamoyl]-1,5-γ-quinide), finding dissociation constants of the albumin-chlorogenic acids and albumin-quinides complexes in the micromolar range, between 2 and 30μM. Such values are comparable with those of the most powerful binders of albumin, and more favourable than the values obtained for the majority of drugs. Interestingly in the case of 3,4-O-dicaffeoyl-1,5-γ-quinide, we have observed the entrance of two ligand molecules in the same binding site, leading up to a first dissociation constant even in the hundred nanomolar range, which is to our knowledge the highest affinity ever observed for HSA and its ligands. The displacement of warfarin, a reference drug binding to HSA, by the quinide has also been demonstrated.

Synthesis of all stereoisomers of cognac lactones via microbial reduction and enzymatic resolution strategies

Abstract Both enantiomers of the diastereomeric cognac lactones have been synthesised using enzyme assisted reactions in the enantiodifferentiating step. This was accomplished by bakers yeast reduction of their precursors 3-methyl-4-oxononanoic acid and ester and by enzymatic hydrolysis of the latter. An inhibition of hydrolases by the products was observed. Trans -(+)-, trans -(−)-, cis -(+)- and cis -(−)-cognac lactones having 99, 88, 88 and 99% e.e., respectively, were thus obtained. Their CD spectra have also been studied.

Bicyclic γ-butyrolactones. Relation between conformation of the lactone ring and chiroptical properties

Abstract The CD curves of a set of condensed γ-butyrolactones have been investigated. A simple correlation between the sign of the Cotton effect (CE) and the configuration of C α can be deduced from the resulting data.

A facile route to (+)- and (–)-trans-tetrahydro-5-oxo-2-pentylfuran-3-carboxylic acid, precursors of (+)- and (–)-methylenolactocin

The enantioselective synthesis of the title γ-lactone intermediates is easily achieved by employing Porcine pancreas lipase catalysed hydrolysis of the corresponding esters as the key step.

Interaction of coffee compounds with serum albumins. Part II: Diterpenes

Cafestol and 16-O-methylcafestol are diterpenes present in coffee, but whilst cafestol is found in both Coffea canephora and Coffea arabica, 16-O-methylcafestol (16-OMC) was reported to be specific of only C. canephora. The interactions of such compounds, with serum albumins, have been studied. Three albumins have been considered, namely human serum albumin (HSA), fatty acid free HSA (ffHSA) and bovine serum albumin (BSA). The proteins interact with the diterpenes at the interface between Sudlow site I and the fatty acid binding site 6 in a very peculiar way, leading to a significant change in the secondary structure. The diterpenes do not displace reference binding drugs of site 2, but rather they enhance the affinity of the site for the drugs. They, therefore, may alter the pharmacokinetic profile of albumin - bound drugs.

Synthesis of enantiomerically pure bicyclic condensed δ-lactones via microbial reduction and enzymic resolution strategies

Abstract The formation of enantiopure δ-lactones condensed with alicyclic rings has been achieved either by reduction with bakers yeast of the corresponding δ-keto esters and δ-keto acids or by enzymic resolution of the former compounds. The absolute configurations of the lactones were determined by means of CD spectroscopy, using the correlation method.

Baker's yeast reduction of cyclic δ-ketoesters: synthesis and chiroptical properties of condensed δ-lactones

Abstract Enantiomerically pure condensed δ-lactones have been prepared from the corresponding δ-ketoesters by the use of Saccharomyces cerevisiae . The reactions were not only highly enantioselective but also highly diastereoselective, provided the bakers yeast was preincubated at 50°C for 30 min. Interestingly, and contrary to what is usually found, the use of nutrients inhibited the bioreductions. The relative configurational assignments have been made by means of NMR, while the absolute configurations and conformations of the lactone rings were attributed by means of CD studies.

Baker's yeast reduction of 4-hetero-2-(2-nitroethyl)cyclohexanones

Abstract Bakers yeast reduction of 3-(2-nitroethyl)-tetrahydro-4H-pyran-4-one 10 and 3-(2-nitroethyl)-tetrahydro-4H-thiopyran-4-one 11 gave the corresponding optically active cis alcohols with good diastereo- and enantioselectivity. The unreacted optically active ketones were also isolated.

Chemoenzymatic synthesis of optically active 4-methyl-tetrahydro-5-oxo-2-furancarboxylic acids and esters

Abstract Enantiomerically pure 4-methyl-tetrahydro-5-oxo-2-furancarboxylic acids and esters are prepared by enzymatic resolution of the chiral racemic esters. Their stereochemistry as well as their absolute configurations have been established by chemical correlation. The influence of the alkoxycarbonyl group at C-2 and that of the methyl group at C-4 on the sign of the Cotton effect in their CD spectra have been investigated. Formation of enantiomerically pure hydroxydiesters, precursors of the above-mentioned γ-lactones, by baker’s yeast reduction of the corresponding ketodiesters was unsatisfactory.