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Information theory makes it possible to give a semiquantitative graphical representation of the various strategies used to reach a given synthetic target. Skeletal complexity and similarity of the precursors with respect to the target structure provide figures which monitor the progress made from the starting material en route toward the target. Examples selected from the triquinane family are used to illustrate the benefits but also the present limits of such an approach. Whereas for silphinene and hirsutene various synthetic strategies appear in a clear graphical form when treated within this framework, coriolin shows that the skeleton-only approach provides graphics which can be misleading. To improve this limitation, progress will have to be made in the treatment of functional complexity from a synthetic point of view. From a more general point of view, a practical treatment of stereochemistry within the information theory framework is still waited for. The graphical treatment displays clearly the key step(s) in a given strategy. Such steps are often characterized by a large change in complexity and/or similarity. This semiquantitative representation converges with, on one hand, the interest of some rearrangements in shorter synthesis and, on the other hand, the interest and the limits of the class of reactions variously christened as cascades, domino, tandem. The treatment shows also the indissociable counterpart of these reaction-centered approaches: the structural entities which make them possible. Such structural entities (holosynthons) call attention to synthetic strategies where a global part (holos: whole) of the target is looked at, this view complements the more classical bond by bond, disconnection approach.Chemists have had intuitive feelings about molecular complexity. In 1981 Bertz 1 developed a quantitative approach based on information theory 2 and graph representation of molecules. 3 In this approach, the molecular complexity is measured as a function of the number and nature of its constitutive atoms and of the number and nature of the constitutive bonds. The overall complexity of the molecule is calculated as being the sum of complexities associated with connectivity factors and complexities associated with the presence of heteroatoms. Hendrickson and Toczko 4 have developed a simple algorithm for calculating this complexity for any organic compound. The results converge with a chemist's intuition on many structural features: a cyclic compound is considered more complex than its acyclic counterpart; a ramified hydrocarbon is more complex than its linear counterpart; a molecule with several carbons replaced by heteroatoms is more complex.The virtue of this approach is to provide figures allowing easy graphical comparisons of synthetic strategies. We have used it here as a convenient tool for such comparisons. Figure 1 shows on simple examples the convergence of its results with chemical intuition. Its systematic application will also reveal its limits in the analysis to come. If these limits ...

The photodynamic therapy (PDT) efficiency of five phthalocyanines, chloroaluminum phthalocyanine (AlPc), dichlorosilicon phthalocyanine (SiPc), bis(tri-n-hexylsiloxy)silicon phthalocyanine (PcHEX), bis(triphenylsiloxy)silicon phthalocyanine (PcPHE) and nickel phthalocyanine (NiPc), was assessed on two leukemic cell lines TF-1 and erythroleukemic and B lymphoblastic cell lines, Daudi, respectively. AlPc showed the best photocytotoxicity leading to 0.008 surviving fraction at 2 x 10(-9) M for TF-1 and 4 x 10(-9) M for Daudi. A1 5 x 10(-7) M, SiPc and PcHEX induced a significant photokilling, whereas NiPc and PcPHE were inactive. Laser flash photolysis and photoredox properties of the phthalocyanines were investigated to try to relate these parameters with the biological effects. AlPc showed the longest triplet life-time: 484 microseconds in dimethyl sulfoxide/H2O. This value was increased up to 820 microseconds when AlPc was complexed with human serum albumin used as a membrane model. Such an enhancement was not observed with the silicon phthalocyanines. Upon irradiation, all the phthalocyanines generated singlet oxygen with 0.29-0.37 quantum yield values. The reduction potentials of the excited states obtained from measurement in the ground state and energy of the excited triplets show that AlPc is the best electron acceptor. The in vitro photocytotoxicity observed and the measured parameters are in agreement with a key role of electron transfer in PDT assays involving these phthalocyanines.

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