Ian R. Hardcastle

Comparison between inhibition of protein kinase C and antagonism of calmodulin by tamoxifen analogues

A variety of analogues of tamoxifen were tested for inhibition of protein kinase C (PKC) activity in MCF-7 breast cancer cells. These results were compared with the calmodulin antagonism exhibited by the analogues as measured by inhibition of calmodulin-dependent cyclic AMP phosphodiesterase. The same structural features that enhanced PKC inhibition also led to an increase in calmodulin antagonism, namely 4-iodination and elongation of the basic side-chain. The most potent analogue has a 4-iodine substituent and eight carbon atoms in its basic side-chain with IC50 values of 38 microM for PKC inhibition and 0.3 microM for calmodulin antagonism, which compares with 92 and 6.8 microM, respectively, for tamoxifen. Some selectivity was achieved with a ring-fused analogue that retained the potency of tamoxifen as a PKC inhibitor, but lacked calmodulin antagonism.

Synthesis of 6,8-substituted-5,7-difluoro-3,4-dihydro-1H-quinoxalin-2-ones via reductive cyclisation of 2,4,6-substituted-3,5-difluoronitrobenzenes

Abstract The synthesis of substituted 5,7-difluoro-3,4-dihydro-1H-quinoxalin-2-ones is described via reductive cyclisation of 2,4,6-substituted-3,5-difluoronitrobenzenes. Reliable conditions for the reduction of solid-phase bound 2,4,6-substituted-3,5-difluoronitrobenzenes were not found. In contrast, solution-phase reductions proceeded smoothly giving the cyclised quinoxalin-2-one products in good yields. A method optimised for rapid parallel synthesis is described, using zinc in acetic acid as reductant, which has been demonstrated to be general for products bearing a range of substituents.

Solid-phase synthesis of novel inhibitors of Farnesyl Transferase

A novel diphosphate mimic, the 2,3,6-trifluoro-5-hydroxy-4-nitrophenoxy group (1), has been employed as the template in the solid-phase synthesis of novel farnesyl transferase inhibitors using the Mitsunobu reaction. The most potent inhibitor (farnesyloxy-5-hydroxy-2,3,6-trifluoro-4-nitrobenzene) displayed an IC50 of 6.3 microM versus farnesyl transferase.

Synthesis and DNA reactivity of alpha-hydroxylated metabolites of nonsteroidal antiestrogens

Tamoxifen [(E)-1-(4-(2-(N,N-dimethylamino)ethoxy)phenyl)-1, 2-diphenylbut-1-ene], a nonsteroidal antiestrogen, induces liver tumors in rats by a genotoxic mechanism. The mechanism of DNA adduct formation is believed to proceed via the formation of a reactive carbocation at the alpha-position from the alpha-hydroxylated metabolite. Molecular mechanics calculations [Kuramochi, H. (1996) J. Med. Chem. 39, 2877-2886] have predicted that 4-substitution will affect the stability of the carbocation and thus will alter its reactivity toward DNA. We have synthesized the putative alpha-hydroxylated metabolites of 4-hydroxytamoxifen [(E)-1-(4-(2-(N, N-dimethylamino)ethoxy)phenyl)-1-(4-hydroxyphenyl)-3-hydroxy-2-phenyl but-1-ene] and idoxifene [(Z)-1-(4-iodophenyl)-3-hydroxy-2-phenyl-1-(4-(2-(N-pyrrolidino) ethoxy)phenyl)but-1-ene] and compared their reactivities with DNA with that of alpha-hydroxytamoxifen [(E)-1-(4-(2-(N, N-dimethylamino)ethoxy)phenyl)-3-hydroxy-1,2-diphenylbut-1-ene]. As predicted, the bis-hydroxylated compound reacted with DNA in aqueous solution at pH 5 to give 12-fold greater levels of adducts than alpha-hydroxytamoxifen, whereas alpha-hydroxyidoxifene gave one-half the number of adducts. The results demonstrate that idoxifene presents a significantly lower genotoxic hazard than tamoxifen for the treatment and prophylaxis of breast cancer.

Length increase of the side chain of idoxifene does not improve its antagonistic potency in breast-cancer cell lines.

Abstract Linkage of specific residues onto steroidal estrogens through a long aliphatic side chain leads to “pure antiestrogens” devoid of residual estrogenic activity. Therefore, we assessed whether an increase in the length of the side chain of the triphenylethylenic antiestrogen idoxifene might increase its antagonistic potency. Culture of MCF-7 and tamoxifen-resistant variant RTX6 cells in the presence of CB 7675, a (CH2)8 derivative of idoxifene [(CH2)2], ruled out this possibility. This compound partly blocked MCF-7 cell growth only at 10−6 M to almost the same extent as tamoxifen and failed to inhibit the growth of RTX6 cells, whereas the pure antiestrogen RU 58 668 was effective on both cell lines at much lower concentration. This absence of improvement was reflected in the observation of an efficiency for down-regulating progesterone receptor no better than that of tamoxifen. Pure antiestrogens are known to down-regulate the estrogen receptor, whereas triphenylethylenic antiestrogens up-regulate the receptor; CB 7675 behaves as the latter in agreement with its lack of strong antagonistic activity.

Polymer-assisted solution-phase library synthesis of 4-alkoxy-2-hydroxy-3,5,6-trifluorobenzoic acids

Abstract The efficient synthesis of a small library of 4-alkoxy-2-hydroxy-3,5,6-trifluorobenzoic acids is described via the fluoride mediated alkylation of 5,6,8-trifluoro-7-hydroxy-2-methyl-benzo[1,3]dioxin-4-one with a collection of structurally diverse bromoalkanes. The use of ion-exchange resins during the reaction sequence enabled the preparation of the majority of the products in 82–98% purity without the need for chromatography.

Synthesis of the farnesyl ether 2,3,5-trifluoro-6-hydroxy-4-[(E,E)-3,7,11-trimethyldodeca-2,6,10-trien-1-yloxy]nitrobenzene, and related compounds containing a substituted hydroxytrifluorophenyl residue: novel inhibitors of protein farnesyltransferase, geranylgeranyltransferase I and squalene synthase

Pentafluoronitrobenzene was converted via two successive phase-transfer catalysed SNAr reactions with (E,E)-farnesol or geraniol followed by hydroxide ion into the 2,3,6-trifluoro-5-hydroxy-4-nitrophenyl farnesyl ether 3a and the geranyl ether 3b. Analogues containing a cyano (3c) or carbamoyl (3d) group in place of nitro or an epoxygeranyl (3e) group as the prenyl (3-methylbut-2-enyl) containing residue were similarly prepared. Those containing a sulfonic acid (35a, 35b) or a methyl sulfone (41) group were made by modifications of this approach involving the use of protecting groups. The synthesis of carboxy analogues (27a, 27b) involved the alkylation of a protected fluorinated ortho-hydroxybenzoic acid derivative (25) with (E,E)-farnesyl or geranyl bromide. The non-fluorinated compound 18 was analogously prepared via compound 17a. Mitsunobu reactions were used in the synthesis of 15, a dihydroxylated analogue of 3b, and of 8, the non-fluorinated analogue of 3a. The nitro compounds 3a and 3b were moderate inhibitors of both farnesyl transferase and geranylgeranyl transferase I, the geranyl carboxy derivative 27b of the latter enzyme and the farnesyl sulfonic acid derivative 35a of squalene synthase.

Pentafluoronitrobenzene a novel scaffold for the solid-phase synthesis of 2,4,6-substituted-3,5-difluoronitrobenzene libraries

The use of pentafluoronitrobenzene as a scaffold for solid-phase synthesis of 2,4,6-substituted-3,5-difluoronitrobenzenes is described. The scaffold is amenable to the synthesis of structurally diverse combinatorial libraries. Primary and secondary amines can be introduced to the scaffold via three successive nucleophilic aromatic substitutions under increasingly forcing conditions. The synthesis of a 36-member validation library is described as follows. Displacement of the para-fluorine was achieved in solution with a set of primary and secondary amines. Following purification, the para-substituted scaffold was attached to an amino acid-loaded hydroxymethylbenzyloxypolystyrene resin via a second substitution of one of the ortho-fluorines. The final reactive ortho-fluorine was then displaced by a second set of amines. After cleavage from the solid support the library was furnished in good overall purity, as determined by LCMS.

4′-Substituted analogues of idoxifene: Antiestrogens and calmodulin antagonists

Abstract 4′-substituted analogues of the antiestrogen idoxifene have been prepared. All the compounds were assayed for antagonism of calmodulin dependent c-AMP phosphodiesterase and for binding to rat uterine estrogen receptor. The 4′-amino compound was the most potent antiestrogen (RBA = 47) whilst retaining a similar calmodulin antagonism to idoxifene.