Synthesis of Optically Pure 3,4-Disubstituted l-Glutamates from a Novel 2,3-Aziridino-γ-lactone 4-Carboxylate Derivative

Gabriel-Cromwell aziridination of amino sugars; chiral ferrocenoyl-aziridinyl sugar synthesis and their biological evaluation

N-sugar substituted chiral aziridines were synthesized via Gabriel-Cromwell reaction. Novel pure diastereomers of aziridine derivatives (4 diastereomers) were readily obtained in high yields and their structures were confirmed by means of 1H NMR, 13C NMR, FT-IR, Mass and optical rotations. This is, to the best of our knowledge, the unique example of N-sugar aziridine synthesis. Diastereomeric effects for prostate (PC3) and cervix (HeLa) cancers were screened and it has been observed that the epimers bearing the same sugars showed different results against PC3 and HeLa cancer cells. The novel sugar aziridines were investigated as promising prodrug candidates for prostate cancer (PC3) therapy. Moreover, the drug likeness calculations (Lipinski's rule, physicochemical properties, lipophilicity, solubility, pharmacokinetics and bioavailability radar) have indicated that the sugar aziridines can be good candidates as oral drugs.

Synthesis of chimera oligopeptide including furanoid β-sugar amino acid derivatives with free OHs: mild but successful removal of the 1,2-O-isopropylidene from the building block

Complementary to hydrophobic five membered ring β-amino acids (e.g. ACPC), β-sugar amino acids (β-SAAs) have found increasing application as hydrophilic building blocks of foldamers and α/β chimeric peptides. Fmoc-protected β-SAAs [e.g. Fmoc-RibAFU(ip)-OH] are indeed useful Lego elements, ready to use for SPPS. The removal of 1,2-OH isopropylidene protecting group increasing the hydrophilicity of such SAA is presented here. We first used N3-RibAFU(ip)-OH model compound to optimize mild deprotection conditions. The formation of the 1,2-OH free product N3-RibAFU-OH and its methyl glycoside methyl ester, N3-RibAFU(Me)-OMe were monitored by RP-HPLC and found that either 50% TFA or 8 eqv. Amberlite IR-120 H+ resin in MeOH are optimal reagents for the effective deprotection. These conditions were then successfully applied for the synthesis of chimeric oligopeptide: -GG-X-GG- [X=RibAFU(ip)]. We found the established conditions to be effective and-at the same time-sufficiently mild to remove 1,2-O-isopropylidene protection and thus, it is proposed to be used in the synthesis of oligo- and polypeptides of complex sequence combination.

Furan-Derived Chiral Bicycloaziridino Lactone Synthon: Collective Syntheses of Oseltamivir Phosphate (Tamiflu), (S)-Pipecolic acid and its 3-Hydroxy Derivatives

A unified synthetic strategy for oseltamivir phosphate (tamiflu), (S)-pipecolic acid, and its 3-hydroxy derivatives from furan derived common chiral bicycloaziridino lactone synthon is described here. Key features are the short (4-steps), enantiopure, and decagram-scale synthesis of common chiral synthon from furan and its first-ever application in the total synthesis of biologically active compounds by taking the advantages of high functionalization ability of chiral synthon.

Synthesis of nonracemic hydroxyglutamic acids

Glutamic acid is involved in several cellular processes though its role as the neurotransmitter is best recognized. For detailed studies of interactions with receptors a number of structural analogues of glutamic acid are required to map their active sides. This review article summarizes syntheses of nonracemic hydroxyglutamic acid analogues equipped with functional groups capable for the formation of additional hydrogen bonds, both as donors and acceptors. The majority of synthetic strategies starts from natural products and relies on application of chirons having the required configuration at the carbon atom bonded to nitrogen (e.g., serine, glutamic and pyroglutamic acids, proline and 4-hydroxyproline). Since various hydroxyglutamic acids were identified as components of complex natural products, syntheses of orthogonally protected derivatives of hydroxyglutamic acids are also covered.

Exploring human adenosine A3 receptor complementarity and activity for adenosine analogues modified in the ribose and purine moiety

In this paper we investigated the influence on affinity, selectivity and intrinsic activity upon modification of the adenosine agonist scaffold at the 3'- and 5'-positions of the ribofuranosyl moiety and the 2- and N6-positions of the purine base. This resulted in the synthesis of various analogues, that is, 3-12 and 24-33, with good hA3AR selectivity and moderate-to-high affinities (as in 32, Ki=27 nM). Interesting was the ability to tune the intrinsic activity depending on the substituent introduced at the 3'-position.

Enantiospecific Total Synthesis of (−)-Polyoxamic Acid Using 2,3-Aziridino-γ-lactone Methodology

The non-natural enantiomer of polyoxamic acid was synthesized in six steps from 2,3-aziridino-gamma-lactone 7 with an overall yield of 10%. The key step of the strategy is a deprotection-protection sequence on the nitrogen atom of the aziridine ring required for aziridine activation toward nucleophilic ring opening.

First enantiospecific synthesis of a 3,4-dihydroxy-L-glutamic acid [(3S,4S)-DHGA], a new mGluR1 agonist

The first synthesis of one of the 4 possible stereoisomers of 3,4-dihydroxy-L-glutamic acid ((3S,4S)-DHGA 3), a natural product of unknown configuration, is described. The synthesis is based on the Lewis acid catalyzed reaction of benzyl alcohol with a D-ribose-derived 2,3-aziridino-gamma-lactone 4-benzyl carboxylate (6). Preliminary pharmacological studies showed that (3S,4S)-3 is an agonist of metabotropic glutamate receptors of type 1 (mGluR1) and a weak antagonist of mGluR4 but has no discernible activity with respect to mGluR2. This activity profile can be rationalized by fitting extended conformations of (3S,4S)-3 in proposed models of each of these receptor subtypes.

Enantiospecific Syntheses of Valienamine and 2-epi-Valienamine(1)

Cyclic sulfite 10, readily available from (-)-quinic acid (3) in 10 steps, was ring opened regio- and stereospecifically with azide anion to give (1S,2R,3R,4R)-1-azido-3,4-di-O-benzyl-5-(benzyloxymethyl)cyclohex-5-ene-2,3,4-triol (11). Deprotection of 11 afforded, for the first time, 2-epi-valienamine (2), which was isolated as penta-N,O-acetyl-2-epi-valienamine (14). The configuration of the free hydroxy group in 11 was inverted by a two-step sequence to give the blocked valienamine 19 that was deprotected to give valienamine (1), isolated as penta-N,O-acetylvalienamine (21). This approach furnished (+)-valienamine (1) in 16 steps (7% overall yield) and recorded the first synthesis of 2-epi-valienamine (2) in 13 steps (11% overall yield).

Synthesis of Vicinal Amino Alcohols via a Tandem Acylnitrene Aziridination-Aziridine Ring Opening

A facile synthesis of differently substituted vicinal amino alcohols is reported. We have demonstrated that these amino alcohols could be readily prepared from the oxazolidinones by treatment with aqueous base. We have synthesized a variety of substituted bicyclic aziridine precursors from the corresponding azidoformates using an intramolecular aziridination reaction. The nucleophilic ring opening of these bicyclic aziridines using carbon, oxygen, nitrogen, sulfur, and halogen-containing nucleophiles provided the oxazolidinones in good yield with high regioselectivity. In all cases, nucleophilic attack occurred exclusively at the least substituted carbon of the aziridine ring. Consequently, our approach allows for convenient and rapid access to the vicinal amino alcohol functionality, an important structural component of many natural products.

2,3-Aziridino-2,3-dideoxy-D-ribono-gamma-lactone 5-Phosphonate: Stereocontrolled Synthesis from D-Lyxose and Unusual Aziridine Ring Opening

The synthesis of (1R,4S,5S)-N-(benzyloxycarbonyl)-4-[(diethoxyphosphinyl)methyl]-3-oxa-6-azabicyclo[3.1.0]hexan-2-one (23), a new member of the 2,3-aziridino gamma-lactone family of compounds, was achieved in 15 steps from D-lyxose. Like all aziridino gamma-lactones known so far, 23 reacted with a soft nucleophile (ethanethiol) to give exclusively the product of aziridine ring opening at C-2 (24). On the other hand, hard nucleophiles (alcohols) did not react directly with the aziridine ring of 23 but appeared to promote intramolecular attack of the aziridine ring at C-3 by the C-5 phosphonate group, resulting, after hydrolytic workup, in formation of the 2-amino-3-hydroxy-D-ribono-1,4-lactone derivatives 25 and 26, instead of the expected 2-amino-3-alkoxy-D-xylono-1,4-lactone derivatives.