Axial chiral metallocenes by two-fold ring-closing metathesis.

Novel doubly bridged metallocenes have been prepared by remarkably selective two-fold alkene ring-closing metathesis. The solid state structures of 3 and 5 reveal 1,2',3,4'-connectivity and screw-shaped geometry of the molecules.

Effect of histamine in sinus node arrested with reserpine.

Histamine restored spontaneous activity in the isolated rabbit sinus node arrested with reserpine. This fact suggests that catecholamines are not the unique activators of adenylate cyclase required for cardiac pacemaking, and may be replaced by histamine.