A Straightforward Synthesis of N-Boc-L-serinal and N-Boc-L-threoninal Acetonides

Ethynylglycine synthon, a useful precursor for the synthesis of biologically active compounds: an update: part I: preparations of ethynylglycine synthon

The ethynylglycine synthon {(R)-2,2-dimethyl-3-(tert-butoxycarbonyl)-4-ethynyloxazolidine} is a chiral compound with valuable synthetic interest. An update on the different routes for its synthesis is reviewed and discussed.

Supramolecular Assembly of an Amphiphilic GdIII Chelate: Tuning the Reorientational Correlation Time and the Water Exchange Rate

We report the synthesis and characterization of the novel ligand H(5)EPTPA-C(16) ((hydroxymethylhexadecanoyl ester)ethylenepropylenetriaminepentaacetic acid). This ligand was designed to chelate the Gd(III) ion in a kinetically and thermodynamically stable way while ensuring an increased water exchange rate (kappa(ex)) on the Gd(III) complex owing to steric compression around the water-binding site. The attachment of a palmitic ester unit to the pendant hydroxymethyl group on the ethylenediamine bridge yields an amphiphilic conjugate that forms micelles with a long tumbling time (tau(R)) in aqueous solution. The critical micelle concentration (cmc = 0.34 mM) of the amphiphilic [Gd(eptpa-C(16))(H(2)O)](2-) chelate was determined by variable-concentration proton relaxivity measurements. A global analysis of the data obtained in variable-temperature and multiple-field (17)O NMR and (1)H NMRD measurements allowed for the determination of parameters governing relaxivity for [Gd(eptpa-C(16))(H(2)O)](2-); this is the first time that paramagnetic micelles with optimized water exchange have been investigated. The water exchange rate was found to be kappa(298)(ex) = 1.7 x 10(8) s(-1), very similar to that previously reported for the nitrobenzyl derivative [Gd(eptpa-bz-NO(2))(H(2)O)](2-) kappa(298)(ex) = 1.5 x 10(8) s(-1)). The rotational dynamics of the micelles were analysed by using the Lipari-Szabo approach. The micelles formed in aqueous solution show considerable flexibility, with a local rotational correlation time of tau(298)(l0) = 330 ps for the Gd(III) segments, which is much shorter than the global rotational correlation time of the supramolecular aggregates, tau(298)(g0) = 2100 ps. This internal flexibility of the micelles is responsible for the limited increase of the proton relaxivity observed on micelle formation (r(1) = 22.59 mM(-1) s(-1) for the micelles versus 9.11 mM(-1) s(-1) for the monomer chelate (20 MHz; 25 degrees C)).

Ethynylglycine synthon from Garner’s aldehyde: a useful precursor for the synthesis of non-natural amino acids

The ethynylglycine synthon, namely (R)-2,2-dimethyl-3-(tert-butoxycarbonyl)-4-ethynyl-oxazolidine, can be obtained through the synthetic elaboration of naturally occurring serine. This compound has been exploited as a helpful and versatile non-racemic building block to be used for the design and synthesis of biologically important compounds, mainly non-natural alpha-amino acids. Taking advantage of the terminal acetylene moiety several synthetic applications can be designed. Metalation followed by trapping with electrophiles or Cu/Pd catalysed coupling with aromatic halogenides are shown to deliver useful precursors of ethynylglycine derivatives. Additions of bimetallic reagents like stannyl- or silylcuprates are useful entries for the regio- and stereoselective functionalization of the lateral chain, aimed at the synthesis of modified vinylglycine precursors. An overview of our recent work in the field will be given, and the use of ethynylglycine synthon in the synthesis of non-racemic saturated and unsaturated non-natural amino acids will be briefly reviewed.

Efficient synthesis of a configurationally stable l-serinal derivative

An efficient synthesis of a configurationally stable l-serinal derivative 8 was achieved using an N-hydroxymethyl group in about 50% overall yield in four steps from l-serine. Not more than 1% racemization was observed during the preparation of 8. Its enantiomeric integrity was maintained for at least 15 days at room temperature, and it was stable on silica gel. The orthogonal protective groups of 8 would make it a useful chiral synthon.

The total syntheses of D-erythro-sphingosine, N-palmitoylsphingosine (ceramide), and glucosylceramide (cerebroside) via an azidosphingosine analog

The total synthesis of D-erythro-sphingosine (9) was performed by a chirospecific method starting from D-galactose via an azidosphingosine intermediate to give highly homogeneous (>99.9% C18:1) sphingosine base (9) which contained no observable olefin isomerization by product and was demonstrated to be optically pure by a novel method utilizing Mosher's acid. Ceramide (10) was prepared from this sphingosine (9) with highly homogeneous (99.8% C16:0) palmitic acid by two methods. The cerebroside glucosylceramide (23) was the next sphingolipid in this series to be synthesized in a highly homogeneous form. These three sphingolipids are currently being used for biophysical studies of the structures of their hydrated bio-molecular assemblies.

Preparation and Synthetic Applications of (S)- and (R)-N-Boc-N,O-isopropylidene-alpha-methylserinals: Asymmetric Synthesis of (S)- and (R)-2-Amino-2-methylbutanoic Acids (Iva)

This report describes an efficient and convenient large-scale synthesis procedure for (S)- and (R)-N-Boc-alpha-methylserinal acetonides (3 and 4) starting from (R)-2-methylglycidol 5. The application of both of these compounds as valuable chiral building blocks in the asymmetric synthesis of alpha-methylamino acids is also demonstrated by the synthesis of (S)- and (R)-isovalines (Iva) (6 and 7).