In this critical review, the ring opening of non-activated 2-substituted aziridines via intermediate aziridinium salts will be dealt with. Emphasis will be put on the relationship between the observed regioselectivity and inherent structural features such as the nature of the C2 aziridine substituent and the nature of the electrophile and the nucleophile. This overview should allow chemists to gain insight into the factors governing the regioselectivity in aziridinium ring openings (81 references).

The ring opening of 2-alkyl-substituted 1,1-di(arylmethyl)-and 1-methyl-1-(1-phenylethyl)aziridinium salts by fluoride, chloride, bromide and iodide in acetonitrile has been evaluated for the first time in a systematic way, affording regioisomeric mixtures of primary and secondary fluorides, whereas the corresponding secondary β-chloro, β-bromo and β-iodo amines were obtained as the sole reaction products through regiospecific ring opening at the substituted position. Both experimental and computational results revealed a product stability-dictated reaction outcome through thermodynamic control in the chloride, bromide and iodide case, involving rearrangement of the initially formed primary halides to the more stable secondary halides. The ring opening of the same aziridinium salts by fluoride, however, was shown to be mediated by steric interactions (kinetic control), furnishing the corresponding primary β-fluoro amines as the main reaction products. Only for 2-acylaziridinium ions, the reaction outcome was shown to be under full substrate control, affording secondary β-fluoro, β-chloro, β-bromo and β-iodo amines through exclusive attack at the activated -carbonyl carbon atom.

inner-sphere mode to the phosphate group, one may conclude that probably the larger part (or even all) of the 46 ± 10% of Cu-(AMP)cl (Table VI) is present as a pure inner-sphere macrochelate, i.e., in the form of structure (iii).The possible occurrence of structure (ii) with N-7 outer sphere coordinated via a water molecule and direct metal ion-phosphate binding should not lightly be dismissed. There is evidence for the formation of such species in M(ATP) systems,7 **1•12•13 and it is well known60•63 that N-7 has a pronounced tendency to form hydrogen bonds to water molecules. Should there be traces of closed species present in the alkaline earth ion systems, like Mg(AMP)cl (Table

Sphingosine 1-phosphate (S1P), a product of sphingosine kinases (SphK), mediates diverse biological processes such as cell differentiation, proliferation, motility and apoptosis. In an effort to search and identify specific inhibitors of human SphK, the inhibitory effects of synthetic sphingoid analogs on kinase activity were examined.Among the analogs tested, we found two, SG12 and SG14, that have specific inhibitory effects on hSphK2. N,N-Dimethylsphingosine (DMS), a well known SphK inhibitor, displayed inhibitory effects for both SphK1 and SphK2, as well as protein kinase C. In contrast, SG12 and SG14 exhibited selective inhibitory effects on hSphK2. Furthermore, SG14 did not affect PKC. In isolated platelets, SG14 blocked the conversion of sphingosine into sphingosine 1-phosphate significantly. This is the first report on the identification of a hSphK2-specific inhibitor, which may provide a useful tool for studying the biological functions of hSphK2.2

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