Sergio Sandri

A new synthesis of both the enantiomers of 4-amino-3-hydroxybutanoic acid (gabob) and mm2 calculations for rotamers of the intermediate oxazolidin-2-on

Abstract The easy Chromatographic separation of the diastereomertic mixture of oxazolidin-2-ones 4a and 4b allows to synthesize pure R-(-)- la and (S)-(+)-GABOB 1b . The 1H NMR pattern of 4a and 4b can be correlated with the configuration at C-5 and this relationship is confirmed by MM2 calculations for rotamera of 5-substituted oxazolidin-2-ones.

A simple asymmetric synthesis of (+)- and (−)-2,6-diaminopimelic acids

Abstract The asymmetric synthesis of both the enantiomers of 2,6-diaminopimelic acid (2,6-DAP) has been accomplished starting from the chiral synthon 1.

A new approach to the synthesis of enantiomerically pure 2,3-diaminoacids through chiral imidazolidin-2-ones

Abstract The synthesis of enantiomerically pure 5-iodomethylimidazolidin-2-ones ( 3a–c ) and ( 4a–c ) is reported, by means of iodocyclisation of allylic tosylureas ( 2a–c ). Starting from pure ( 3a ) and ( 4a ), a synthesis of both (R)- and (S)-2,3-diaminopropanoic acid is described. Furthermore the cyclisation of the homoallylic tosylurea ( 2d ), occurring with total diastereoselection, is depicted.

Synthesis of (3R,6R)- and (3S,6S)-3,6-dialkylpiperazin-2,5-dione derivatives as useful intermediates to both (R) and (S) α-aminoacids

Abstract The alkylation of 2 leads to a diastereomeric mixture where 4 is generally present in greater amounts than 3 . The successive alkylation of 4 affords exclusively the cis derivative 7 , while a cis/trans mixture is obtained from isomer 3 . In alkaline solution, the trans isomer 6 suffers a total conversion into a 1:1 mixture of the cis isomers 5 and 7 easily separated by silica gel chromatography. The configurations of the introduced stereogenic centers at C-3 and C-6 have been assigned on the basis of 1 H-NMR spectroscopic data. Cleavage of heterocyclic ring of 5 and 7 leads to the corresponding ( R )- and ( S )-α-aminoacidsrespectively. Therefore, the substrate 2 appears a very useful chiral template to synthetize enantiomerically pure α-amino acids.

Synthesis of chiral 1,2-diamines

Abstract (1′S,5R,S)-(1′-phenyleth-1′-yl)-5-iodomethyl-imidazolines 4a,b have been synthesised and easily resolved by silica gel chromatography. The correlation between the configuration and the 1H NMR chemical shifts allows to assign the configuration at the C-5 of these intermediates. Each pure diastereomer has been converted to R(−)- and to S(+)-1,2-propyldiamine, respectively.

Synthesis of compounds containing the isoprene unit : A stereospecific synthesis of dehydronerol isovalerate, a component of anthemis Montana L

Abstract A stereospecific synthesis of dehydronerol isovalerate, isolated from the roots of Anthemis montana L., utilising the dianion of 3-methyl-2-butenoic acid is described.

A new approach to 2-phenylthioalcohols in high optical purity

Abstract 2-Phenylthioalcohols are prepared in high optical purity by alkylation of chiral imides of 2-phenylthioacetic acid, obtained starting from chiral imidazolidin-2-ones.

A novel, efficient synthesis of (±)-erythro-sphingosine

Abstract A stereoselective synthesis of (±)-erythro-sphingosine triacetate ( 1 ) is described. The key reaction that determines the right stereochemistry is the iodocyclization of 1-trichloroacetimido-(2E,4E)-octadecadiene ( 5 ). The 4,5-dihydro-l, 3-oxaztne ( 6 ) through cleavage with HC1 and treatment with Amberlyst A 26 in the AcO- form, followed by full acetylation, affords ( 1 ) in good yield.

Unusual peptides containing the 2,6-diaminopimelic acid framework: Stereocontrolled synthesis, X-ray analysis, and computational modelling. Part 2

Abstract The stereocontrolled synthesis of peptides 6, 9 and 14, structural variants of 2,6-diaminopimelic acid, was carried out starting from the chiral synthon 1, easily obtained from l -valine. The configuration of the introduced stereogenic centres has been assigned on the basis of 1H NMR spectroscopic data. X-Ray crystal structure and conformation analysis of 5 are also reported.

Stereoselective synthesis of α,α′-diamino-dicarboxylic acids. Part 2☆

Abstract Enantiomerically pure α,α′-diamino-dicarboxylic acids ( R , R )- 4 , ( S , S )- 5 and ( S , S )- 7 have been synthesized starting from the glycine-derived chiral synthon ( S , S )- 1 .