Acylated guanidines

Acyl-Guanidine werden durch Lithiumalanat zu Alkyl-guanidinen reduziert (s.S. 

Auf gleiche Weise werden auch N-Acyl-guanidine umgesetzt, wobei aus dem abgekiihlten Reaktionsgemisch die 1,2,4-Oxadiazole bereits auskristallisieren. Die Ausbeuten sind gut bis vor-... 

The polar functionality presents a major problem in the synthesis of cylindrospermopsin because the natural product cannot be extracted into organic solvents, making its separation from water-soluble reagents difficult. Clearly, the sulfate ester should be introduced in the last step. The guanidine should also be introduced late in the synthesis and should be protected as a less basic acyl guanidine until as late as possible. Finally, the uracil is also polar and so must be either introduced late in the synthesis or protected as a dialkoxypyrimidine. 

Acyl guanidines have pKa values in the order of 7 whereas simple guanidines have pKa values of approximately 13. This increased acidity favors the formation of hydrogen-bonded ion pairs and hence increases the binding affinity. 

In order to obtain alkyl-, aryl- and acyl- guanidines Wang linker is treated with carbonylimida-zole and thiourea consecutively. The displacement of sulfur by primary or secondary amines leads to acid-labile carbamate linkage [119]. 

There have been no systematic studies for systems (63)-(74). Derivatives of (68), containing the acyl guanidine moiety of fixed conformation have been prepared, and UV and IR have been used to examine the conformational and tautomeric preference of acylguanidines <85JCS(P2)1255, 85JCS(P2)1265>. 

The drug, a structural combination of cilostamide [211] and anagrelide (155), is a potent and selective inhibitor of cyclic AMP phosphodiesterase. The acyl guanidine unit is both weakly basic (pK 3.5) and weakly acidic (pKa 11.3), but the solubility of the compound is too low for it to be physiologically useful [209, 212]. 

A series of acyl guanidines has been synthesized as BACE-1 inhibitors. The impact of various substituents has been investigated, and these efforts have culminated in the identification of several acyl guanidines with potent BACE-1 inhibitory activity. The synthesis and SAR of these compounds will be presented. 

Mixed carbonic anhydrides, acyl guanidine, N-acylimidazoles, N-acyl-N -methylimidazolium chloride and acyl phosphates are other agents that have been used to esterify starch in water [65-76]. Starch esters containing carboxylic acid group have been prepared by reaction with cyclic dibasic anhydrides [65]. 

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