Giuseppe Guanti

Enantiospecific and diastereoselective synthesis of anti α-hydrazino- and α-amino-β-hydroxyacids through “electrophilic amination” of β-hydroxyesters

Abstract β-Hydroxyesters 1a–1d were transformed into corresponding dianions and condensed with di-t-butylazodicarboxylate to give anti protected α-hydrazino-β-hydroxyesters 2a–2d with good diastereoselectivities (up to 94:6). Cleavage of protecting groups followed by ester hydrolysis gave the previously unknown anti α-hydrazino-β-hydroxyacids 4a–4d, which were in turn converted by hydrogenolysis into anti α-amino-β-hydroxyacids 5a–5d. Starting from (S) 1a, enantiomerically pure (2S, 3S) allo-threonine 5a was obtained in good overall yields. On the contrary, reaction of silyl ketene acetal 10, derived from 1a, with a diazonium salt furnished predominantly the syn isomer, but in unsatisfactory yield.

Diastereoselection in trimethylsilyl trifluoromethanesulphonatecatalyzed reaction of silyl ketene acetals with imines

Abstract The trimethylsilyl trifluoromethanesulphonate catalyzed condensation of silyl ketene acetals with imines afforded β-amino esters with prevalent anti relative diastereoselectivity (up to 100%). Some anti β-amino esters have been then cyclized to trans β-lactams.

Enzymes in asymmetric synthesis: Effect of reaction media on the PLE catalysed hydrolysis of diesters

Abstract Organic cosolvents and other addenda aan influence fhe rate and the enantioselectivity of pig liver esterase catalysed hydrolysis of meso diacetates and diesters, the magnitude of the effect being strongly dependent on the nature of substrate.

Enzyme catalyzed monohydrolysis of 2-aryl-1 3-propanediol diacetates. A study of structural effects of the aryl moiety on the enantioselectivity

Abstract PPL catalyzed monohydrolysis of 2-aryl substituted 13-propanediol diacetates afforded the corresponding monoacetates in acceptable to fair chemical and optical yields. Electronic effects in the aromatic ring were examined. Elaboration of some 2-arylpropanediol monoacetates to optically active 2-arylpropanols and propanoic acids was performed.

Microbiological synthesis of variously protected L-glyceraldehydes in high optical purity

Abstract Variously protected L-glyceraldehydes have been enantioselectively synthesized through a sequence involving acylation of formylanion equivalents with glycolic acid derivatives followed by bakers yeast mediated reduction of the resulting ketones.

Short synthesis of protease inhibitors via modified Passerini condensation of N-Boc-α-aminoaldehydes

Extension of the previously reported modification of Passerini multicomponent reaction (involving condensation with N-Boc-α-aminoaldehydes followed by a deprotection–transacylation step) to α-aminoacid derived carboxylic or isocyanide components, allowed the highly convergent and short synthesis of complex peptidomimetic structures, including known potent inhibitors of serine proteases.

Application of tandem Ugi multi-component reaction/ ring closing metathesis to the synthesis of a conformationally restricted cyclic pentapeptide

A conformationally restricted cyclic pentapeptide, containing an unsaturated 9-membered lactam as a semi-rigid scaffold, was prepared in a very convergent manner, through tandem Ugi reaction/ring closing metathesis.

Enzymatic asymmetrization of some prochiral and meso diols through monoacetylation with pig pancreatic lipase (PPL)

Abstract Monoacetates 1–8 and 10–11 , derived from asymmetric monoesterification of prochiral or meso diols, have been obtained in good to excellent enantiomeric excess by using inexpensive crude PPL supported on celite, and vinyl acetate as both solvent and acylating agent. Under these conditions reactions are fast and reproducible, and the enzyme can be recycled.

Stereoselective preparation of synthetic equivalents of 2-deoxy-2-amino- and 3-deoxy-3-aminotetroses from malic acid. Application to the synthesis of C18-D-ribo-phytosphingosine

Abstract “Electrophilic amination” of β-hydroxyester 5, derived from (S) malic acid, with di- t -butylazodicarboxylate allowed preparation of new synthetic equivalents of 2-deoxy-2-amino- and 3-deoxy-3-amino-tetroses. As an application, D- ribo -C 18 -phytosphingosine was stereoselectively synthesized.

Enzymes as selective reagents in organic synthesis: Enantioselective preparation of “asymmetrized tris (hydroxymethyl)methane”

Abstract A new C-4 chiral building block, that is a tris (hydroxymethyl)methane derivative where the three equivalent hydroxymethyl groups have been differentiated [(THYM)*], was prepared with excellent enantioselection, through PPL catalysed monohydrolysis of prochiral diacetate 3.