CrossRef enabled

PAC Archives

Archive →

Pure Appl. Chem., 2012, Vol. 84, No. 11, pp. 2289-2298

Published online 2012-05-22

Imitation and modification of bioactive lead structures via integration of boron clusters

Sven Stadlbauer1, René Frank1, Matthias Scholz1, Solveig Boehnke1, Verena M. Ahrens2, Annette G. Beck-Sickinger2 and Evamarie Hey-Hawkins1*

1 Institute of Inorganic Chemistry, Universität Leipzig, Johannisallee 29, D-04103 Leipzig, Germany
2 Institute of Biochemistry, Universität Leipzig, Brüderstraße 34, D-04103 Leipzig, Germany

Abstract: In medicinal chemistry, carbaboranes can be employed either as boron carriers for boron neutron capture therapy (BNCT) or as scaffolds for radiodiagnostic or therapeutic agents. We have developed a suitable synthesis employing the phosphoramidite method to connect meta-carbaboranyl bis-phosphonites with the 6'-OH group of isopropylidene-protected galactose, followed by oxidation or sulfurization to give the corresponding bis-phosphonates. Deprotection yielded water-soluble compounds. The corresponding disodium salts exhibit especially low cytotoxicity. Preliminary results on the in vivo toxicity and biodistribution of two compounds in mice indicated a lack of selectivity for the cotton rat lung (CRL) tumor chosen for the experiment. For the incorporation of carbaboranes into breast tumor-selective modified neuropeptide Y, [F7, P34]-NPY, a synthesis of a carbaborane-modified lysine derivative was developed. Linkage of the lysine to the boron cluster was achieved by using a propionic acid spacer. Incorporation of the amino acid derivatives into NPY and [F7, P34]-NPY by solid-phase peptide synthesis was successful. Preliminary studies showed that the receptor binding affinity and signal transduction of the boron-modified peptides were very well retained. Asborin, the carbaborane analogue of aspirin, is a rather weak inhibitor of cyclooxygenase-1 (COX-1) and COX-2, but a highly potent aldo/keto reductase 1A1 (AKR1A1) inhibitor. Modification either at the carboxyl group or at the chlorophenyl ring in indomethacin with ortho- and meta-carbaboranyl derivatives gave active derivatives only for the ortho-carbaborane directly attached to the carboxyl group, while the corresponding adamantyl and meta-carbaboranyl derivatives were inactive.