Amino groups s. a. Amines Replacement

It was postulated (320) that replacing the cf the physostigmine molecule with a methylene group would increase the molecule s chemical and metabolic stability by conversion of the potentially less stable aminal group to a more stable amino group. A series of 8-carbaphysostigmine congeners (253) was studied, in which R was H or CH3 R was CH3,... 

It is known, however, that isothiocyanates on their own can form stable self-assembled monolayers on gold (Section V.E), and amine-terminated monolayers were reported to show unusually low reactivity towards electrophilic reagents329,330. It is therefore possible that the observed immobilization of eosin is due not to reaction with amino groups, but to either insertion of the eosin isothiocyanate into a disordered layer of cysteamine, or even replacement of cysteamine monolayer with the molecules of S=C=N—eosin. Because the experimental data on reactions in gold-thiol monolayers are scarce, chemical transformations described in this section should be interpreted with some caution. 

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