Der Auserwählte: Die Desymmetrisierung von meso‐2 gelingt mithilfe von Diethylzink in Gegenwart von 10 Mol‐% des CuI‐Komplexes von 1. 1 wurde als bester Ligand aus einer Bibliothek von 125 Verbindungen ermittelt; einige andere Liganden aus derselben Bibliothek liefern bevorzugt das Enantiomer 4.

The chosen one: The desymmetrization of meso‐2 is possible with the use of diethylzinc in the presence of the CuI complex of 1 (10 mol %; Tf=CF3SO2). Ligand 1 was optimized from a screen of a library of 125 compounds. Other ligands from the same library favor the formation of the opposite enantiomer 4.

[reaction: see text] A highly regio-, diastereo-, and enantioselective desymmetrization of five-, six-, and seven-membered meso-cyclic allylic bis-diethyl phosphates (2a, 2b, and 2c, respectively) was obtained with diethylzinc, using catalytic amounts of [Cu(OTf)](2).C(6)H(6) and phosphoramidite ligands 5. Enantiomeric excesses of up to 87, 94, and >98% were obtained for the addition of diethylzinc to cyclopentene, cyclohexene, and cycloheptene bis-diethyl phosphates, respectively.

A highly regio-, diastereo-and enantioselective desymmetrization of five-, six-, and seven-membered meso, cyclic allylic bis(diethyl phosphates) (3-5) with organozinc reagents was developed, using catalytic amounts (10 mol%) of [Cu(OTf)] 2 ·C 6 H 6 and two different classes of chiral ligands: Schiff bases 1 and phosphoramidites 2. Good to excellent enantioselectivities were obtained for every substrate by a subtle balance of ligand structure and experimental conditions. In particular, ee's of up to 88 % were obtained for the fivemembered ring substrate 3 with ligands 1cjo and 1cjm using Et 2 Zn (94 % ee with Me 2 Zn, 88 % ee with nBu 2 Zn). Schiffbase ligands 1 were not effective with the six-and seven-

We have previously shown that when administered to mice without adjuvant, a chimeric peptide consisting of the fusion peptide F from measles virus protein linked at the C-terminus of a cytotoxic T-cell epitope from the M2 protein of respiratory syncytial virus efficiently primes for an major histocompatibility complex (MHC) class-I restricted cytotoxic T lymphocyte (CTL) response. In this report, we demonstrated by microspectrofluorometry that the fusion-peptide moiety bound to the plasma membrane of living cells. When the fusion peptide was linked to the C-terminus of the CTL epitope, the chimeric peptide (M2-F) adopted a marked /I-sheet conformation. In contrast, when the fusion peptide was linked to the N-terminus of the T-cell epitope (F-M2), the chimeric peptide adopted an a-helical conformation in the presence of tritluoroethanol. The immunogenicity of the two chimeric peptides for class-I restricted CTL was also significantly different, the one adopting the a-helical conformation being more immunogenic. Probably due to its obvious conversion to an a-helical conformation, the F-M2 peptide could have a higher propensity to insert into membranes, as shown by rnicrospectrofluorometry, with a resultant better immunogenicity than the M2-F peptide.