Piero Grasselli

On the steric course of baker's yeast mediated reduction of alkyl 4-azido- and 4-bromo-3-oxobutyrate. Synthesis of (R)- and (S)-carnitin

Abstract Bakers yeast reduction of ethyl 4-azido- and 4-bromo-3-oxobutyrate affords (3 R ) (8) and (3 S ) (2), respectively, in high optical purity.

Immobilized penicillinacylase: Application to the synthesis of the dipeptide aspartame

Abstract Immobilized penicillinacylase efficently catalyzes the conversion at pH 7.5 of N-phenacetyl aspartame ( 4 ) into aspartame ( 2 ) and phenylacetic acid.

Immobilized benzylpenicillin acylase: Application to the synthesis of optically active forms of carnitin and propranalol

The hydrolysis at pH 7.5 in the presence of immobilized benzylpenicillin acylase of the N-phenacetyl derivatives of the primary amines (3)-(5) affords the hydroxy amines (6)-(8), key intermediates in the synthesis of optically active forms of carnitin and propranalol, of ca. 0.4, 0.3 and 0.8 ee, respectively.

Enantioselective synthesis of β-substituted butyric acid derivatives via orthoester Claisen rearrangement of enzymatically resolved allylic alcohols: application to the synthesis of (R)-(−)-baclofen

Abstract A three step synthesis of (R)-(−)-baclofen is described. The key step is the orthoester Claisen rearrangement of enantiopure allylic alcohol (S,E)-(−)- 1a , affording γ,δ-unsaturated ester (S,E)-(+)- 6 with high stereoselectivity. This latter derivative is converted into ( R )-(−)-baclofen through a high yield one-pot reaction.

On the steric course of addition of Grignard reagents onto α,β-dialkoxy erythro and threo chiral aldehydes. Synthesis of (+) and (−)-exo and endo-brevicomin

Addition of BrMgCH2CH3 onto the erythro and threo aldehydes (1) and (2) to form (3)+(6) and (9)+(10) proceeds with 6:4 and 8:2 threo-erythro selectivity, respectively. From (3) and (6), (2S) and (2R)-2-benzyloxy butyraldehyde (13) and (14) have been prepared. Addition of onto (13) and (14) proceeds with 6:4, threo-erythro selectivity, to give after preparative gas chromatographic separation, the enantiomeric forms of exo- and endo- brevicomin (19), (21) and (20), (22).

On the steric course of the addition of diallylzinc onto α,β-dialkoxy chiral carbonyl compounds: stereospecific synthesis of 2,6-dideoxysugars of the L-series

Abstract The synthesis of the 2,6-dideoxy sugars L -digitoxose (14), 2-deoxy- L -fucose (15) and L -mycarose (16) from the C4 and C5 chiral synthons (1), (2) and (3), through the intermediacy of the C7 adducts (4), (8) and (12), obtained by erythro addition of diallylzinc onto (1), (2) and (3), is reported.

Substrate specificity and enantioselectivity of penicillinacylase catalyzed hydrolysis of phenacetyl esters of synthetically useful carbinols

Abstract Penicillinacylase from E.coli , immoblized on Eupergit C beads catalyzes the hydrolysis in water/CH 3 CN 10:1, at pH 7.5 and 23° C, of a set of O-phenylacetate esters of primary carbinols. The highest enantioselectivity is observed in the case of the 2,2-dimethyl-1,3-dioxolane-4-methanols structurally related to the penicillin (1) framework. Minor modifications of this basic structure are not altering the acceptability by the enzyme, but significantly decrease the enantioselectivity of the hydrolysis, as does the use of benzene as solvent and sepharose-bound enzyme.

Stereochemistry of the yeast - mediated conversion of delta 2 - decenolide into delta decanolide

Abstract NMR studies on δ-decanolide samples obtained from 1 and 5 in reduction experiments with bakers yeast in D 2 O and H 2 O, respectively, show that the double bond saturation involves beta re-face trans formal addition of hydrogen atoms, arising to a large extent from water. The reduction does not depend on the absolute configuration at position 5 and shows a kinetic preference for the ( R ) enantiomer.

Synthesis of N-benzoyl-L-daunosamine from D-threonine

Abstract The synthesis of N-benzoyl- L -daunosamine (14) from the C4 threo aldehyde (2b), prepared from D -threonine, through the intermediacy of the C7 adduct (7a) is reported

Enzyme-Mediated Synthesis of (S)- and (R)-Verapamil

A lipase-mediated synthesis of (S)- and (R)-verapamil is described. The key steps of the synthetic sequence are the enantioselective acetylation, mediated by Lipase PS, of allylic alcohol (Z)-(±)-2, affording the acetate derivative (Z,R)-(−)-3 (ee 92%) and the Ireland−Claisen rearrangement of this latter and of its enantiomer (Z,S)-(+)-3 (ee 92%) to afford acid derivatives (E,R)-(−)-4 (ee 94%) and (E,S)-(+)-4 (ee 93%), precursors of (S)- and (R)-verapamil, respectively.