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In the process of finding new drug candidates medicinal chemists nowadays have a variety of options to choose from, one is to apply combinatorial chemistry techniques. Since the early 1990's synthetic and analytical methods as well as new technologies have been growing rapidly in the area of combinatorial chemistry. Applying these techniques have resulted in the production of large numbers of compounds. A trend is observed towards smaller libraries of compounds with more drug-like properties. An analysis is made to establish the contribution of combinatorial chemistry in providing new lead candidates for (pre)clinical development towards new pharmaceutical products. Ten representative examples are given to describe the impact of ombinatorial chemistry on different levels of the lead discovery and optimization process. Furthermore, reports on combinatorial chemistry products that are already in (pre)clinical development were traced back to their source. The interim analysis showed only limited success of combinatorial chemistry approaches in terms of delivering leads. Second generation libraries appear more drug-like and focussed and may result in more compounds entering clinical studies in the future.

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Binding of the stable melanocortin(4-9) analogue, Org2766 [Met(O2)-Glu-His-Phe-D-Lys-Phe] to cultured rat sciatic nerve Schwann cells was demonstrated using a biotinylated derivative in semiquantitative histochemical and CELISA assays. Org2766 bound to Schwann cells, but not to fibroblasts, and was displaced maximally by unlabeled Org2766, alpha-MSH and ACTH(1-24). Displacement of Org2766 from the binding sites was considerably reduced by N- and C-truncation of the peptide. Specific binding of Org2766 was also demonstrated in the immortal rat Schwann cell line SCL4.1/F7 and was more pronounced in cells displaying a differentiated morphology. Org2766 and alpha-MSH increased cyclic AMP content of Schwann cells but neither stimulated DNA synthesis when applied alone. However, in the presence of a priming (subthreshold) concentration of the mitogen, cholera toxin, Org2766 and alpha-MSH caused a delayed increase in DNA synthesis. Org2766 did not modulate the expression of several differentiation-related Schwann cell markers. However, Org2766 increased immunoreactivity for p75 low-affinity NGF receptor on Schwann cells and evoked the release of neurotrophic factor(s) that synergized with NGF in stimulating neurite outgrowth in rat DRG neurons. The results indicate that Schwann cells are a primary target for the action of Org2766 and provide evidence for an indirect mechanism by which melanocortins might stimulate neurite sprouting in regenerating peripheral nerve axons.

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To study the putative binding sites of the neurotrophic peptide Org 2766, an analogue of ACTH(4-9) [H-Met(O2)-Glu-His-Phe-D-Lys-Phe-OH], biotinylated forms of the peptide were used. After fixation, cultures of rat spinal cord and dorsal root ganglia were incubated with 4-10 microM of biotinyl-Org 2766 (b-Org 2766). Binding of both N- and C-terminally biotinylated Org 2766 was seen to phase-bright, round cells with thin processes, but not to flat, orthogonal-shaped cells with tapering processes. The b-Org 2766 binding was displaceable by an excess of nonbiotinylated Org 2766. Light and electron microscopy showed that the biotinylated peptide binds to a cytoplasmatic component as well as to the cell membrane. Double-labeling experiments with b-Org 2766 and an antibody (RT-97) to a high molecular weight neurofilament protein in dorsal root ganglion cultures showed, using fluorescence and confocal scanning laser microscopy, that all b-Org 2766 binding cells were neurofilament positive. Biotinylated Org 2766 did also bind to the neuronally differentiated cells in cultures of the human neuroblastoma cell line SK-N-SH, but not to those differentiated into epithelial cells. The present data suggest that the neurotrophic peptide Org 2766 binds specifically to cell types with neuronal characteristics.

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The in vitro antiviral and antitumor activities of (-)-debromoeudistomin K (1a) and 10 structural analogues (1b-1j and 11) were evaluated. The synthesis was accomplished with an intramolecular Pictet-Spengler condensation reaction as the key step. This examination revealed some structural and stereochemical features that are important for both the antiviral and antitumor activities. The most striking points for activity are the necessity to have the correct natural stereochemistry at both C(1) and C(13b) and the presence of the C(1)-NH2 substituent. As was revealed before with naturally isolated eudistomins a substituent in the indole ring greatly influences the biological activity. The 5-OMe derivative 1h shows high potency in both antiviral and antitumor models.

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