Synthesis and evaluation of 4,5-dihydro-5-methylisoxazolin-5-carboxamide derivatives as VLA-4 antagonists.

A novel set of compounds containing a 4,5-dihydro-5-methylisoxazoline have been successfully designed as VLA-4 receptor antagonists. Compound (14p) had a high receptor binding affinity of 4 nM and also found to be metabolically stable in vitro.

Estrogenic diazenes: heterocyclic non-steroidal estrogens of unusual structure with selectivity for estrogen receptor subtypes.

Estrogens regulate many biological functions, often acting in a tissue-selective manner. Their tissue-selective action is believed to involve differential estrogen action through the two estrogen receptor (ER) subtypes, ERalpha and ERbeta, as well as differential interaction of the ligand-receptor complexes with promoters and coregulator proteins. In the latter case, selectivity is based on the induction of specific conformations of the ligand-ER complex, conformations that are influenced by the structure of the ligand. Estrogen pharmaceuticals having an ideal balance of tissue-selective activity are being sought for menopausal hormone replacement, breast cancer prevention and therapy, and other actions. To expand on the structural diversity of ER ligands that might show such tissue selectivity, we have prepared a series of diazenes (pyrazines, pyrimidines, and pyridazines) substituted with two to four aryl groups and various short-chain aliphatic substituents. All of the pyrazine and pyrimidines bind to ER, some with high affinity and with a considerable degree of preferential binding to either ERalpha or ERbeta. One pyrimidine and one pyrazine have ERalpha affinity preferences as high as 23 and 9, respectively, and one pyrimidine has an ERbeta affinity preference of 8. The pyridazines, by contrast, are quite polar and have only very low binding affinity for the ER. In cell-based transcription assays, several of the pyrimidines and a pyrazine were found to be considerably more agonistic on ERalpha than on ERbeta. Because these triaryl diazenes have the largest volumes among the ER ligands so far investigated, their high affinity demonstrates the flexibility of the ligand binding pocket of the ERs and its tolerance for large substituents. Thus, these novel heterocyclic ligands expand the repertoire of chemical structures that bind to the estrogen receptor, and they could prove to be useful in elucidating the biological behavior of the two ER subtypes and in forming the basis for new estrogen pharmaceuticals having desirable tissue selectivity.

Aryl cyclopentadienyl tricarbonyl rhenium complexes: novel ligands for the estrogen receptor with potential use as estrogen radiopharmaceuticals.

The need for imaging agents for estrogen receptor positive (ER+) tumors that are both cost effective and widely available, as well as the need for novel radiotherapeutic agents for the treatment of breast cancer, has prompted us to investigate cyclopentadienyl tricarbonyl metal [CpMet(CO)(3), Met=Re, Tc-99m] complexes that bind well to the ER. Thus, we have prepared a series of p-hydroxyphenyl-substituted CpRe(CO)(3) complexes and evaluated them (and, in some cases, their cyclopentadiene precursors) for binding to ER. These compounds constitute a new class of structurally integrated organometallic ligands for ER in which the CpMet(CO)(3 )organometallic unit forms the very structural core of these molecules and thus is necessarily intimately involved in their interaction with the receptor. The CpRe(CO)(3) compounds were prepared by reaction of the lithium salt of the arene-substituted cyclopentadiene with a suitable Re(CO)(3)(+) precursor, followed by deprotection of the methyl ether. The X-ray crystal structure of one of these analogues shows that it has the classical 'piano stool'-like geometry, with the alkyl groups directed upward, away from the tripodyl metal carbonyl base. The aryl-substituted CpRe(CO)(3) complexes that we have prepared all bind to the ER, some with affinity as great as 20% that of the native ligand, estradiol. In general, at least two p-hydroxyphenyl substituents and one to two alkyl groups attached to the organometallic cyclopentadienyl core are needed for high ER affinity. Where we have been able to make comparisons, the metal complexes bind to ER with an affinity greater than their cyclopentadiene precursors. The high affinity of some of these complexes indicates that the bulky Re(CO)(3) unit is able to exploit the considerable volume in the center of the ER ligand binding pocket that is not occupied by most ligands, a consideration that is supported by molecular modeling. The preparation of the best of these agents in technetium-99m labeled form is currently being investigated.