(+)-Hemipalmitoylcarnitinium strongly inhibits carnitine palmitoyltransferase-I in intact mitochondria.

The reaction of the methyl ester of (R)-norcarnitine with 1-bromo-2-heptadecanone produces (+)-6-[(methoxycarbonyl)methyl]-2-pentadecyl-4,4-dimethylmorpholinium bromide, 3, which hydrolyzes to (+)-6-(carboxylatomethyl)-2-pentadecyl-4,4-dimethylmorpholinium (hemipalmitoylcarnitinium, HPC) upon treatment with aqueous sodium hydroxide. Single-crystal X-ray analyses have confirmed the structures of (+)-HPC and 3. (+)-HPC inhibits carnitine palmitoyltransferase (CPT-I) activity for the forward reaction (palmitoyl-CoA + carnitine-->) in intact mitochondria from rat heart and rat liver. (+)-HPC competitively (versus carnitine) inhibits CPT-I activity in both rat heart and liver mitochondria with Ki = 2.8 +/- 0.5 and 4.2 +/- 0.7 microM, respectively. As one of the strongest specific inhibitors of CPT-I, HPC is a potential therapeutic agent in myocardial ischemia and Type II diabetes.

Metabolism of tamoxifen by isolated rat hepatocytes. Identification of the glucuronide of 4-hydroxytamoxifen.

Metabolism of 4-hydroxytamoxifen by hepatocytes isolated from rats administered with phenobarbital and examination by TLC of the components not extractable into ethyl acetate revealed 4-hydroxytamoxifen beta-glucuronide; its identity was confirmed by comparison of its 1H NMR spectrum with that of synthetic material. This conjugate was also formed on metabolism of tamoxifen. It bound to cytosolic oestrogen receptors with only one thousandth the affinity of 4-hydroxytamoxifen and gave a correspondingly very weak inhibition of growth of the MCF-7 human breast cancer cell line. Therefore, in contrast to reported observations on the 3-glucuronide of oestradiol, the MCF-7 cells were unable to hydrolyse 4-hydroxytamoxifen glucuronide and on this evidence, formation of this metabolite is solely a deactivation pathway.

Non-isomerisable antiestrogens related to tamoxifen.

Three types of non-isomerisable antiestrogens analogous to tamoxifen and 4-hydroxytamoxifen are described. Advantages of non-isomerisability are simplified synthesis, simplified metabolism profile, and that structure-activity relationships become more meaningful. The compounds described differ from tamoxifen by having an extra ring methyl group, a fused seven-membered ring system, or the central ethylene linkage saturated. These compounds retained both binding affinity to estrogen receptors and growth inhibition of MCF-7 human breast cancer cells in vitro.

Analogues of tamoxifen: the role of the basic side-chain. Applications of a whole-cell oestrogen-receptor binding assay to N-oxides and quaternary salts.

Derivatives of tamoxifen (1) and 4-hydroxy-2-methyltamoxifen (2) in which the basic side chain has been modified by N-oxidation or by quaternization have been investigated with respect to the effects on affinity for the oestrogen receptor and on cytostatic activity towards the MCF-7 cell line in vitro. In addition to the conventional cytosol assay for receptor binding affinity (RBA) a recently developed whole-cell assay was employed. N-oxidation (e.g. 2----3) produced no significant alteration in RBA value either in cytosol or in whole cells, nor in activity towards the MCF-7 line. Quaternization with methyl iodide (1----4, 2----6) or ethyl bromide (1----5, 2----7b: the cis isomer 7a also formed) did not alter receptor binding in the cytosol assay but almost abolished binding in the whole cell and cytostatic activity. The whole-cell RBA values for 2 (0.45) and 3 (0.5) were lower than those for 4-hydroxytamoxifen (2.9), suggested to be due to the lower oestrogenicity of the 2-methyl derivatives since activity against MCF-7 cells was unimpaired. The even lower values of whole-cell RBA (0.01-0.02) for the quaternary ethyl bromide derivatives 7a and 7b were ascribed to poor penetration into the cell since these compounds had minimal cytostatic activity.

Hydroxy derivatives of tamoxifen.

In the exploration of the structural features that affect the RBA (binding affinity for the estrogen receptor of rat uterus relative to that of estradiol) in the tamoxifen [trans-(Z)-1-[4-[2-(dimethylamino)ethoxy]phenyl ]-1,2-diphenyl-1-butene] series, several derivatives variously substituted in the 1-phenyl group have been synthesized. [In the tamoxifen series, the descriptors E and Z, which define the configuration of the geometrical isomers and depend on the location and nature of substituents in the aromatic moieties and the ethyl group, may vary, although the relative configuration (cis or trans) does not. In order to avoid confusion the terms cis and trans will be used in this paper to refer to the relative positions of the 4-[2-(dimethylamino)ethoxy]phenyl and ethyl (or hydroxyethyl, hydroxypropyl, or bromo) substituents attached to the ethene moiety.] The final stage of each synthesis involved acid-catalyzed dehydration of a tertiary alcohol, and, in contrast to the known 3- and 4-hydroxy derivatives which were obtained as near-equimolar cis,trans mixtures, only the trans forms of the 2-hydroxy, 2-methyl, 2,4-dihydroxy, and 4-hydroxy-2-methyl derivatives were obtained. Also, in contrast to the trans forms of the 3- and 4-hydroxy derivatives, which are readily equilibrated to cis,trans mixtures, the trans 2-hydroxy derivative could not be isomerized. Tamoxifen and 2-methyltamoxifen had similar RBA's (approximately 1% of that of E2), but that of 2-hydroxytamoxifen was much lower (0.1%). Introduction of a second hydroxyl group (2,4-dihydroxy derivative) enhanced the RBA, and for the 4-hydroxy-2-methyl derivative, the RBA and growth inhibitory activity against the MCF-7 mammary tumor cell line in vitro were high and comparable to those of 4-hydroxytamoxifen, a metabolite of the parent drug. Tamoxifen derivatives hydroxylated at positions 3 or 4 of the 1-butene moiety and the 5-hydroxy-1-pentene analogue were also synthesized, but they had very low RBA values.

Structural studies on some tamoxifen derivatives.

The crystal structures of four derivatives of the antiestrogenic drug tamoxifen are described. These are of 2-hydroxy-, 3-hydroxy-, and 2-methyl-4-hydroxytamoxifen and of 1-(4-methoxyphenyl)-2-phenyl-1-[(tetrahydropyran-2-yloxy)phenyl]-1 -butanol, the synthetic precursor to 2-hydroxytamoxifen. All compounds have trans stereochemistry about the ethylene double bond, as in tamoxifen itself. The orientations of the hydroxy substituents have been found to differ by 180 degrees, depending on the nature of the compound. Empirical energy calculations have been used to show that the barrier to free rotation for the hydroxy-substituted phenyl rings is too high for interconversion to take place. These orientational differences are, it is suggested, related to the marked differences in estrogen receptor binding ability.