CONCLUSIONS.

• The complexation capability of any receptor is the direct expression of the degree of preorganization of its binding sites in the free form.

• The preorganization can be investigated by X-ray analysis, but in the case of lipophilic receptors the difficulty of having suitable crystals makes this method useless as it is evidenced by the very few structures known.

• A more versatile way to look at preorganization of binding sites is to have the conformation of minimum energy of the free receptor which can be obtained by "Molecular Mechanic Calculations".

• The results here reported (namely: the very good agreement of X-ray and MM calculation of the free cis 1c) prove that this last statement is true.

• Based on this last statement, the minimum energy conformations calculated for 2c are likely those really present in the solution, and their strong preorganization explain the high complexation capability and selectivity of 2a-b.

REFERENCES.

1. Quici, S. et al. J. Org. Chem. 1988, 53, 5292.
2. Still, W. C. et al. J. Comp. Chem. 1990, 11, 440.
3. Still, W. C. et al. J. Am. Chem. Soc. 1989, 111, 4379.
4. Kollman, P. A. et al. J. Am. Chem. Soc. 1984, 106, 765.
5. Kollman, P. A. et al. J. Comp. Chem. 1986, 7, 230.
6. Molecular Mechanics. ACS Monograph 177; American Chemical Society; Washington, D. C.; 1982.

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