The isosterism concept

CO2 and N2O was later coincidentally acknowledged as both compounds were capable of acting as reversible anesthetics to the slime mold Physarum plycephalum.  

The first example clearly demonstrates that isosterism does not inevitably imply isoelectric structures (having the same total electric charge), but it becomes evident that isoelectronic isosteres show the closest analogies  

In the field of organic chemistry, Langmuir predicted the analogy between diazomethane and ketene, which was only discovered later. 

Proton fixed on surface FIGURE 15.4 The notion of pseudoatoms. 

TABLE 15.2 Hydride Displacement Law In Each Vertical Column the Atom is Followed by its Pseudoatoms 

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B. The isosterism concept atoms or groups A. Structural parameters... 

Starting in 1932, Erlemneyer published a series of detailed studies about the isosterism concept, and particularly. 

Erlemneyer also proposed three expansions of the isosterism concept ... 

Recognizing the usefulness of the isosterism concept in the design of biologically active molecnles, Friedman proposed to call bioisosteres componnds... 

The apparent failure of the isosterism concept for the inactive thiophene, inversed furan and pyrimidine is thus interpretable on a rational basis. In Table 15.10 are listed some more exotic examples of bioisosteric replacements of cyclic systems. 

Starting in 1932, Erlenmeyer published a series of detailed studies on the isosterism concept, and particularly about its first applications to biological problems. Erlenmeyer proposed his own definition of isosteres as elements, molecules or ions in which the peripheral layers of electrons may be considered identical. Erlenmeyer also proposed three expansions of the isosterism concept ... 

In conclusion, it became evident to the physicists that the concept of isosterism, developed before quantum-mechanical theories, could not provide at the molecular level the same results as those that the periodic classification had provided for the elements, namely a correlation between electronic structure and physical and chemical properties. In the field of medicinal chemistry the isosterism concept, taken in its broadest sense, has proved to be a research tool of the utmost importance. The main reason for this is because isosteres are often much more alike in their biological than in their physical and chemical properties. An illustrative example is found in the comparison of oxazolidine-diones and hydantoins which possess different chemical reactivities, but present a similar antiepileptic profile (Fig. 13.2). 

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