Polymer-aided stereodivergent synthesis (PASS): a new concept for the discrete preparation of optical antipodes

[structure: see text]. A new concept for the discrete preparation of optical antipodes is reported. The approach makes use of a cyclization/cleavage procedure that has been applied to polymer-supported quasi-meso compound 1, containing a polymeric leaving group and a regular leaving group. Two-directional cyclization leads to the formation and separation of quasi-enantiomers 2 and 3 simultaneously, with one being immobilized and one free in solution. Treatment of 2 and 3 with appropriate nucleophiles gives discrete enantiomers 4 and 5.

Clathration-induced asymmetric transformation of cefadroxil

[structure: see text] The cephalosporin antibiotic Cefadroxil can be epimerized at the alpha-carbon of its amino acid side chain using pyridoxal as the mediator. By clathration with 2,7-dihydroxynaphthalene, the desired diastereomer can be selectively withdrawn from the equilibrating mixture of epimers. In this way, an asymmetric transformation of Cefadroxil can be accomplished. This opens the possibility of the production of Cefadroxil starting from racemic p-hydroxyphenylglycine, in contrast to the current industrial synthesis that employs the D-amino acid in enantiopure form.

Enantioselective Synthesis of 4-Acetylaminocyclopent-2-en-1-ols from Tricyclo[5.2.1.0(2,6)]decenyl Enaminones. Precursors for 5'-Norcarbocyclic Nucleosides and Related Antiviral Compounds

An efficient synthesis of both (1S,4R) and (1R,4S)-4-N-acetylamino-1-benzoylcyclopent-2-enes 33 has been accomplished starting from enantiopure 5-(1'-phenylethylamino)-endo-tricyclo[5.2.1.0(2,6)]deca-4,8-dien-3-ones 14 and 15. N-Acetylation of both 15 and 14 followed by single electron-transfer reduction using lithium in liquid ammonia afforded diastereomeric mixtures of beta-amino ketones 26 and 27 and of ent-26 and ent-27 in high yields and with high diastereoselectivity. In this reduction process, the enaminone double bond is reduced with the concomitant removal of the alpha-methylbenzyl group as the chiral auxiliary. Thermolysis of the respective diastereomic mixtures of 26 and 27 in the gas phase (FVT) or in solution afforded 4-N-acetylaminocyclopent-2-ene-1-ones 30 in high optical and chemical yields. Acidic hydrolysis of (+)-30 gave (R)-(+)-4-aminocyclopentenone 31 as its hydrochloride. Stereoselective reduction of 30 using sodium borohydride and cerium chloride heptahydrate furnished amido alcohol 32, which was isolated and characterized as its benzoyl derivative 33.

Dose-response of seeds of the parasitic weeds Striga and Orobanche toward the synthetic germination stimulants GR 24 and Nijmegen 1

Striga and Orobanche seeds germinate in response to a host-derived germination stimulant. Dose-response curves of the synthetic strigolactone analogues GR 24 and Nijmegen 1 were determined, and their activities were compared to that of the naturally occurring stimulant sorgolactone. Typical sigmoidal curves were obtained. ED(50) values for GR 24 were in the order of 10(-)(9)-10(-)(8) mol/L; for Nijmegen 1 these values were 3 orders of magnitude higher. Both synthetic stimulants are appreciably active at low concentrations and merit investigation as agents for the suicidal germination approach (i.e., treatment of the soil with stimulant in the absence of a host).

A critical account on the inception of Striga seed germination

The seeds of the parasitic weed Striga germinate in response to stimulants exuded by the roots of host plants and some nonhost plants. Literature data are summarized that support the view that strigolactones induce germination of parasitic weed seeds via a receptor-mediated mechanism. The suggestion by Lynn et al. that the strigol D-ring is solely responsible for germinating Striga seeds via a redox reaction was based on hypothesized structural similarities between the natural compound dihydrosorgoleone (SXSg) and the strigol D-ring. Experiments have shown that the mechanistic connection between SXSg and the strigol D-ring is not valid, and therefore the proposed redox mechanism for the induction of Striga seed germination by strigolactones does not hold.