Abstract: The invention relates to a method of separation by liquid chromatography for preparing enantiomerically pure hetrazines, using cellulose triacetate as a stationary phase and a polar solvent as a mobile phase.

Abstract: A charging valve consisting of a valve sleeve and a valve stem fixed in the interior thereof comprises a valve which acts by compression and tension, the tension or compression being exerted by resilient parts of the valve stem adjacent to both valves.

Abstract: The invention relates to new compounds of general formula ##STR1## wherein R.sub.1 represents an alkyl group,R.sub.2 represents a hydrogen atom, an alkyl group optionally substituted (except at the .alpha. carbon atom) by a hydroxy group, or represents a cycloalkyl group or an allyl, phenyl or benzyl group,R.sub.3 represents an allyl group, an alkyl group optionally substituted (except at the .alpha. carbon atom) by a hydroxy group, or represents a cycloalkyl group orR.sub.2 and R.sub.3 together with the nitrogen atom between them represent a straight-chained alkyleneimino group,the acid addition salts thereof, particularly the acid addition salts thereof with physiologically acceptable inorganic or organic acids which have valuable pharmacological properties, particularly a metastasis-inhibiting effect based on their selective tumour-PDE inhibiting effect, and pharmaceutical compositions containing these compounds or the physiologically acceptable acid addition salts thereof.