Total synthesis of (-)-α-kainic acid via chirality transfer through Ireland-Claisen rearrangement

The total synthesis of (-)-α-Kainic acid is accomplished using a linear strategy involving Noyori asymmetric reduction and chirality transfer through Ireland-Claisen rearrangement as key steps.

Total syntheses of isodomoic acids G and H: an exercise in tetrasubstituted alkene synthesis

A unified approach to the pyrrolidine triacid natural products isodomoic acids G and H has been developed. Total syntheses of both natural products were completed, and determination of the correct stereostructure of isodomoic acid G was established by comparing 5'-(R) and 5'-(S) isomers to a sample of authentic material. A nickel-catalyzed cyclization constructs the pyrrolidine ring while simultaneously establishing either the E or Z stereochemistry of an exocyclic tetrasubstituted alkene. Stereoselective assembly of both the E- and Z-alkenes of the natural products is made possible by a predictable strategy that alters the timing of substituent introduction to control alkene stereochemistry.

Thiopyrophosphoantigens: solid-phase synthesis and in vitro characterization of a new class of Vgamma9 Vdelta2 T cells activators

The Vgamma9 Vdelta2 T cells mediate rapid, innate-like immune responses to pathogens and are important in several key immunoregulatory pathways, including those involved in infections and tumor development. Vgamma9 Vdelta2 T cells respond to low molecular weight isoprenoid phosphoantigens; the prototypic stimulatory compound is isopentenylpyrophosphate (IPP), an alkylphosphate intermediate of mevalonate metabolism that elicits proliferative, cytotoxic, and cytokine secretion responses. We studied the replacement of the pyrophosphate moiety with the thiopyrophosphate bioisostere, synthesizing thioanalogues of IPP and 4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMBPP, the most potent natural antigen known to date). Once their in vitro efficacy and stability had been demonstrated, we synthesized a small library of compounds through the development of an innovative solid-phase strategy. Biological results confirmed thioHMBPP to be the best compound of this first series. Future aims are (i) the exploitation of the parallel solid-phase strategy to further explore structure-activity relationships of this new class of synthetic antigens and (ii) the determination of the PK/PD profile of thioHMBPP.

Synthesis and biological activity of phosphonate analogues and geometric isomers of the highly potent phosphoantigen (E)-1-hydroxy-2-methylbut-2-enyl 4-diphosphate

Gammadelta-T-lymphocytes contribute to innate immunity and are selectively activated by nonpeptide phosphorylated molecules (so-called phosphoantigens) produced by organisms responsible for causing a broad range of infectious diseases. gammadelta-T-cells are also activated by synthetic phosphoantigens and are cytotoxic to tumor cells. Here we report the synthesis, NMR characterization, and comparative biological evaluation of new pyrophosphate, phosphonate, and pyrophosphonate monoesters whose structures correspond to isosteric analogues and stereoisomers of the highly potent isoprenoid metabolite ( E)-1-hydroxy-2-methylbut-2-enyl 4-diphosphate called HDMAPP (hydroxy-dimethyl-allyl pyrophosphate). Both pyrophosphate and pyrophosphonate series elicit promising gammadelta-T-cell stimulatory responses in vitro, the pyrophosphonate ester (C-HDMAPP) being by far more stable than its parent pyrophosphate ester (HDMAPP) with improved ADMET properties and a similar pharmacodynamic profile based on in vivo studies in nonhuman primate. In both series, we found that E-stereoisomers are the most active derivatives and that Z-stereoisomers show very marginal bioactivity levels. These results indicate that the use of bioisosteric analogues of HDMAPP may represent promising new leads for immunotherapy.

Total synthesis of (+/-)-kainic Acid with an aza-[2,3]-Wittig sigmatropic rearrangement as the key stereochemical determining step

A flexible route to the kainoid skeleton is exemplified by the synthesis of (+/-)-kainic acid from 3-butyn-1-ol. The route relies on the aza-[2,3]-Wittig sigmatropic rearrangement to efficiently install the relative stereochemistry between C2-C3. The C4 stereocenter was derived from a diastereocontrolled iodolactonization. The aza-[2,3]-Wittig rearrangement potentially allows structural diversity at C3 and the displacement of the tosyloxy group with retention of stereochemistry allows structural diversity at C4. The trans-C2 carboxylic acid functional group was found to be the most important for retention of stereochemistry at C4 upon treatment with a higher order cyano cuprate reagent.

Stereoselective Synthesis of (+/-)-alpha-Kainic Acid Using Free Radical Key Reactions

Thiol-mediated free radical isomerization of a deliberately substituted but-3-enyl isocyanide 12a, and n-Bu(3)SnH/AIBN-mediated free radical cyclization of a deliberately substituted but-3-enyl isothiocyanate 22, afforded, respectively, the (ethylthio)pyrroline 13a and the thiopyroglutamates 5 and 23. Reduction, protection, and deprotection of these heterocyclic compounds afforded proline derivatives 6 and 25 which contain all the structural elements of alpha-kainic acid (1) except the C-2 acetic acid moiety. These intermediates were stereospecifically converted into (+/-)-alpha-kainic acid using a new method of temporary sulfur connection. Accordingly, CH(2)CO(2)Me is linked to the chiral isopropenyl anchor and then intramolecularly connected to the pyrrolidine ring and eventually disconnected from its anchor by a sequential reductive double elimination process in which the isopropenyl double bond is restored.