Ally1 aryl ethers which have no strongly electron attracting substitueuts undergo a charge-induced [3s, 3s] sigmatropic rearrangement in the prescence of 0.7 mole boron trichloride in chlorobenzene at low temperature, to give after hydrolysis the corresponding 0-ally1 phenols (Tables 1 and 2). The charge induction causes an increase in the reaction rate relative to the thermal Claisen rcarrangement of N 1O1O. With the exception of sllyl 3-methoxyphenyl ether (5). m-substituted allyl aryl ethers show similar behaviour (with respect to the composition of the product mixture) t o that observed in the thermal rearrangement (Table 3). The rearrangement of allyl aryl cthcrs wnth an alkyl group in the o-position, in the presencc of boron trichloride, yields a mixture of 0-and p-ally1 phenols, where more p-product is present than in the corresponding 1)

The binding reaction between purified human platelet glycoprotein IIb-IIIa and fibrinogen was investigated by real-time measurements using the surface-plasmon-resonance sensor technology. In these experiments, either glycoprotein IIb-IIIa or fibrinogen was immobilized on a sensor surface. The time-dependent change in surface coverage that occurred immediately upon contact with a solution of the complementary protein was then detected. The ability to record this dynamic event from its initiation allowed the collection of kinetic and thermodynamic data over an extended time period. These data indicated that initially, in fast reaction, a reversible low-affinity complex with an equilibrium dissociation constant, Kd, of 155-180 nM was formed. In a subsequent slower reaction this complex was transformed into a more stable high-affinity complex with a Kd of 20-70 nM. Efficient dissociation of the high-affinity complex could only be induced in the presence of a competitive inhibitor such as RGDV. These data demonstrate that the binding between glycoprotein IIb-IIIa and fibrinogen is not a single monophasic reaction, but is composed of at least two consecutive processes both with their own kinetics.

Several synthetic sequences for the preparation of 'Platelet Activating Factor' (la), for the corresponding enantiomeric compound (l'a) as well as for the 'Lysocompounds' (lb and l'b) are described.The use of glycerolacetonide 2'a (from D-Mannitol) for the preparation of l'a and l a is presented together with the synthesis of some analogues of l'a and l a . Structural assignment and optical purity of the compounds prepared are confirmed. 1. Einleitung. -Wahrend in letzter Zeit Phospholipide vor allem in ihrer Rolle als Bausteine der Zellmembranen Beachtung fanden, sind neuerdings mit dem 'Platelet Activating Factor' (PAF) [ 11 einerseits, und dem 'Antihypertensive Polar Renomedullary Lipid' (APRL) [2] andererseits, zwei physiologisch hochwirksameVerbindungen als Phospholipide erkannt worden. Beide Verbindungen erwiesen sich als Glycerylather-Phospholipide der Struktur A mit n vorwiegend = 17 und die weitgehende Strukturidentitat (abgesehen von verschiedenen Anteilen unterschiedlich langer Atherketten) der beiden Substanzen scheint gesichert, wie auch die Gleichartigkeit der physiologischen Wirkung: Verbindung l a (mit n = 17) zeigt sowohl plattchenaktivierende wie antihypotensive Wirkung und wird deshalb vereinfachend meist als ( (PAFN bezeichnet [312). )sn-Nomenklatur; sn = stereospecific numbering system: Das C-Atom des Glyceringeriistes in pro-S-Stellung ist C( 1) (s. IUPAC-IUB Commission on Biochemical Nomenclature, Biochim. Biophys. Acta 152, 1 (1968)). Die Anwesenheit von Spuren solcher hochaktiver Verbindungen in bestimmten, aus natiirlichen Quellen isolierten Phospholipiden konnte erklaren, dass die physiologische Wirksamkeit solcher Praparate bei der synthetisch hergestellten Verbindung haufig nicht bestatigt werden konnten (41. 2,

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