摘要：

The acid sphingomyelinase (aSMase) is emerging as an important drug target for a variety of diseases. Inhibition of aSMase prevents bacterial infections in a rat model of cystic fibrosis and formation of acute lung injury (ALI) elicited by endotoxin, acid instillation, or platelet-activating factor (PAF). Moreover, aSMase is essential for infection of non-phagocytotic cells with Neisseria gonorrhoeae and formation of pulmonary emphysema. Pharmacological or genetic inhibition of aSMase prevents apoptosis and degeneration of liver cells in a mouse model for Wilson s disease. In addition, there are several reports that aSMase significantly contributes to the formation of atherosclerotic plugs. This promising progress in aSMase research, based on sophisticated animal models and cultured cells from patients, is thwarted, however, by the lack of potent and selective inhibitors of this enzyme. Phosphatidylinositol-3,5-bisphosphate (PtdIns3,5P2), to date the most potent inhibitor (KM = 0.53 mm), is not suitable for cell culture studies, because of its fivefold negative charge and its two long fatty acid chains which cause it to stack in cellular membranes. Last but not least, this inhibitor is labile towards phospholipases A1, A2, C, and D and phosphoinositide phosphatases. The aSMase is a soluble lysosomal sphingolipid hydrolase, which constitutively degrades sphingomyelin from internalized membrane fragments. Upon stimulation, however, a portion of this enzyme can be found on the outer side of the plasma membrane. This membrane-associated enzyme shows biochemical activity in serum and urine and has been termed secretory sphingomyelinase (sSMase), although it is virtually identical to the lysosomal variant. Its activity is elevated in several diseases. The secretory form of aSMase is believed to play an important role in signal transduction, since it alters the composition of the plasma membrane within putative sphingolipidand cholesterol-rich membrane microdomains. These so-called "lipid rafts" have been suggested to act as "signaling platforms", and there is significant evidence that the cleavage of sphingomyelin to ceramide can dramatically alter the biophysical properties of the putative rafts. In addition, it is well established that ceramide is a potent inductor of apoptosis, which is the main reason for cell degeneration in many of the diseases mentioned above. However, it is unknown whether ceramide acts by remodeling the plasma membrane or by interacting with proteins like cathepsin B, which is involved in cellular signaling. Beside aSMase, two cytosolic, magnesium-dependent and membrane-bound neutral sphingomyelinases (nSMase1 and nSMase2) and an alkaline sphingomyelinase are known, whose cellular function is rather unclear. Recently nSMase has been shown to be essential for the formation of exosomes, lipid vesicles that play a key role in the infection by retroviruses. In contrast to aSMase, there are some potent small-molecule inhibitors for nSMase. Our attempts at synthesizing phosphonate analogues of PtdIns3,5P2 as potential inhibitors of aSMase yielded only moderately active substances. However, we also gained access to a collection of (bis)phosphonates that had been synthesized in the GDR Academy of Sciences and that contained some compounds that are structurally related to our phosphoinositide analogues. When we initially tested these substances at a concentration of 20 mm, we were surprised that some of them were potent inhibitors of aSMase (Tables 1 and 2). Among these substances, a-amino-

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