Antifertility agents. 38. Effect of the side chain and its position on the activity of 3,4-diarylchromans

Dr. Nitya Anand: The Visionary Behind Saheli and the Advances in Medicinal Chemistry

Dr. Nitya Anand was a leading figure in Indian pharmaceutical research. His career spanned several decades, during which he significantly contributed to advancement in drug development and public health. His innovation of Centchroman (Saheli), the world's first non-steroidal oral contraceptive pill, changes the course of contraception use in India. He had done groundbreaking work in leprosy treatment, synthetic peptides, and antibiotics. With over 400 publications and 130 patents, he supervised over 100 PhD students. His work has been recognized with many prestigious awards, including the Padma Shri and the National Nehru Science Award, which have left a long-lasting impact on medicinal chemistry and public health.

The role of the methoxy group in approved drugs

The methoxy substituent is prevalent in natural products and, consequently, is present in many natural product-derived drugs. It has also been installed in modern drug molecules with no remnant of natural product features because medicinal chemists have been taking advantage of the benefits that this small functional group can bestow on ligand-target binding, physicochemical properties, and ADME parameters. Herein, over 230 methoxy-containing small-molecule drugs, as well as several fluoromethoxy-containing drugs, are presented from the vantage point of the methoxy group. Biochemical mechanisms of action, medicinal chemistry SAR studies, and numerous X-ray cocrystal structures are analyzed to identify the precise role of the methoxy group for many of the drugs and drug classes. Although the methoxy substituent can be considered as the hybridization of a hydroxy and a methyl group, the combination of these functionalities often results in unique effects that can amount to more than the sum of the individual parts.

Simultaneous determination of centchroman and tamoxifen along with their metabolites in rat plasma using LC-MS/MS

AIM

Tamoxifen and centchroman are two non-steroidal, selective estrogen receptors modulators, intended for long term therapy in the woman. Because of their wide spread use, there is a possibility of co-prescription of these agents.

MATERIALS & METHODS

We studied the probable pharmacokinetic interaction between these agents in breast cancer model rats. A simple, sensitive and rapid LC-ESI-MS/MS method was developed and validated for the simultaneous determination of tamoxifen, centchroman and their active metabolites.

RESULTS

The method was linear over a range of 0.2-200 ng/ml. All validation parameters met the acceptance criteria according to regulatory guidelines.

CONCLUSION

LC-MS/MS method for determination of tamoxifen, centchroman and their metabolites was developed and validated. Results show the potential of drug-drug interaction upon co-administration these two marketed drugs.

Nuclear receptors and their selective pharmacologic modulators

Nuclear receptors are ligand-activated transcription factors and include the receptors for steroid hormones, lipophilic vitamins, sterols, and bile acids. These receptors serve as targets for development of myriad drugs that target a range of disorders. Classically defined ligands that bind to the ligand-binding domain of nuclear receptors, whether they are endogenous or synthetic, either activate receptor activity (agonists) or block activation (antagonists) and due to the ability to alter activity of the receptors are often termed receptor "modulators." The complex pharmacology of nuclear receptors has provided a class of ligands distinct from these simple modulators where ligands display agonist/partial agonist/antagonist function in a tissue or gene selective manner. This class of ligands is defined as selective modulators. Here, we review the development and pharmacology of a range of selective nuclear receptor modulators.

Synthesis and in vivo evaluation of 11-substituted estradiol derivatives as anti-implantation agents

Synthesis of 11-substituted estradiol derivatives (12-17) has been carried out by the Grignard reaction with alkyl, allyl, and benzyl halides on 17beta-hydroxy-3-methoxy-11-oxo-estra-1,3,5(10),8(9)-tetraene (10). The novel compounds (10 and 12-17) were evaluated for their preliminary post-coital contraceptive (anti-implantation) activity in Sprague-Dawley rats. The tested compounds were administered orally and showed significant anti-implantation activity. Compound 13 is the most potent compound in the series which showed 100% contraceptive efficacy at 1.25 mg kg(-1).

Diaryl naphthyl methanes a novel class of anti-implantation agents

Diaryl naphthyl methanes and the corresponding 1, 2, 3, 4- and 5, 6, 7, 8-tetrahydro naphthyl methane derivatives have been synthesized as novel estrogen receptor binding ligands. The secondary and tertiary amino alkoxy derivatives of diaryl naphthyl and tetrahydro naphthyl methane interact with the estrogen receptor to elicit promising estrogenic, antiestrogenic and implantation inhibition activities in rats. The most active compounds in this series are 7, 9 and 20, cent percent active in preventing implantation in rats at 2.5 mgkg(-1) dose.

Evaluation of interaction potential of certain concurrently administered drugs with pharmacological and pharmacokinetic profile of centchroman in rats

Centchroman (Ormeloxifene) is a nonsteroidal, selective estrogen receptor modulator, oral contraceptive and anticancer agent, and is intended for long-term use by women. In view of its vast clinical application and the interaction of steroidal oral contraceptives with certain commonly used therapeutic agents, evaluation of interaction of certain concomitantly administered therapeutic agents (ibuprofen, rifampicin, diazepam, salbutamol, nifedipine, paracetamol, haloperidol, and tetracycline), in terms of both the postcoital contraceptive efficacy and pharmacokinetic profile, with centchroman was undertaken in female Sprague-Dawley rats. Among the representatives from each commonly used therapeutic category, interaction (pharmacokinetic) was observed with ibuprofen (60 mg/kg, twice daily), haloperidol (0.7 mg/kg, twice daily), and tetracycline (140 mg/kg, twice daily) coadministration on Days 1 through 5 postcoitum. Of these three therapeutic agents, only tetracycline interfered with the contraceptive efficacy of centchroman. It reduced the bioavailability of centchroman and its active metabolite by increasing their excretion through bile and feces. Increased metabolite excretion on tetracycline coadministration indicates the enterohepatic recirculation of the metabolite, not the parent drug. However, the effect of tetracycline was negated by the inclusion of lactic acid bacillus spores in the regimen.

Pharmacological profile of 6,12-dihydro-3-methoxy-1-benzopyrano[3,4-b] [1,4]benzothiazin-6-one, a novel human estrogen receptor agonist

Pharmacological studies were carried out to characterize further the endocrinological profile and the binding mode to the estrogen receptor (ER) of 6,12-dihydro-3-methoxy-1-benzopyrano[3,4-b][1,4]benzothiazin-6-one (1). Binding experiments were conducted with highly purified recombinant human estrogen receptors hERa and beta. Potent estrogenic activity of compound 1 was assessed by testing its ability to down-regulate ERs and to enhance estrogen receptor element (ERE)-dependent transcription. The latest step of our work dealt with the synthesis of the 9-fluorinated derivative 15 for ionic microscopy experiments to determine the intracellular localization of compound 1. Although 1 failed to compete with [3H]E2 for binding to both ER isoforms, evidence was reported that it interacted with hERalpha in MCF-7 cells (ER down-regulation/ERE-dependent luciferase induction). Hence, an appropriate conformation of the hormone binding domain, most probably conferred by co-regulators of ER, is required for the onset of an activity of the compound 1. Estrogenic activity was weak but on the order of magnitude of that of coumestrol (slightly weaker). The synthesis of the 9-methoxylated derivative 16 and its pharmacological evaluation led us to propose a binding mode of 1 on hERalpha. Compound 1 appears to interact with ERa mainly through interactions of its 3-methoxy substituent with the residue His-524 of the hormone binding domain.

Centchroman, a selective estrogen receptor modulator, as a contraceptive and for the management of hormone-related clinical disorders

DL-Centchroman (67/20; INN: Ormeloxifene) synthesized at the Central Drug Research Institute, Lucknow, is a nonsteroidal once-a-week oral contraceptive. It was introduced in Delhi in July, 1991, marketed in India in 1992 as Saheli and Choice-7 (Hindustan Latex Ltd., Thiruvananthapuram) and Centron (Torrent Pharmaceuticals India Ltd., Ahmedabad), and included in the National Family Welfare Programme in 1995.5 According to post-marketing surveillance, approximately 100,000 women were using this pill and approximately 1100,000 menstrual cycles were covered until 1996. It is a unique need-oriented contraceptive being effective when taken immediately after coitus or routinely as a weekly pill and has the advantage of less frequent administration. Its contraceptive action is quickly reversible. It has long terminal serum halflife of 168 hr in women and exhibits duration of anti-implantation/estrogen antagonistic action of 120 hr, despite a short (24.1 hr) serum halflife, in the rat. In lactating women, it is excreted in milk in quantities considered unlikely to cause any deleterious effect on suckling babies. In phase II and III multicentric trials as a contraceptive, children born of method-and-user failure pregnancies showed normal milestones, without any congenital anomaly. Reports of its promising action in the management of certain hormone-related clinical disorders are available. It has an excellent therapeutic index and is considered safe for chronic administration.

Optimization of contraceptive dosage regimen of Centchroman

Centchroman (Ormeloxifene), a non-steroidal oral contraceptive, is used at a dose of 30 mg once a week. To prevent failures in the beginning of the therapy, it is recommended that a dose of 30 mg twice a week for 12 weeks be administered to build up adequate blood levels. The present study was undertaken to simplify the dosing schedule without sacrificing the purpose of twice a week dosing regimen, using modeling and measurement approaches. The drug was given to 60 female volunteers who were divided into seven groups: group I, 30 mg weekly; group II, 30 mg twice a week; group III, 30 mg twice a week for 12 weeks followed by 30 mg weekly; group IV, 30 mg twice a week for 6 weeks followed by 30 mg weekly; group V, 60 mg weekly; and groups VI and VII, single 60 mg loading dose followed by 30 mg weekly doses. The blood samples were collected and analyzed by HPLC. In group I, mean trough concentrations of centchroman and its active metabolite, 7-desmethyl centchroman, were comparable to the steady-state trough concentrations in groups III, IV, VI, and VII. The metabolite to parent drug ratio remained constant in all the groups. The pharmacokinetic parameters in group VII were comparable to those reported after a single 30 mg dose. Dosage regimen VI was more convenient and provided better pregnancy protection (Pearl index 1.18; unpublished report) than regimen III, which is currently on the market and, thus, could be effectively used for contraception.

Simultaneous liquid chromatographic determination of centchroman and its 7-demethylated metabolite in serum and milk

A precise and sensitive high-performance liquid chromatographic assay was developed and validated for determination of centchroman (I) and its 7-demethylated metabolite (II) in human serum and milk. The serum, at alkaline pH, was extracted with diethyl ether. In the case of milk, after precipitation of the milk protein with acetonitrile, the supernatant was evaporated to dryness and then extracted with diethyl ether at alkaline pH. After solvent evaporation the residue was reconstituted in mobile phase. Separations were accomplished by reversed-phase liquid chromatography using a Spheri-5 cyano column. Recoveries of I and II were always > 95%. Excellent linear relationships (r > 0.999) were obtained between the measured and added concentration ratios of the corresponding serum and milk concentrations over a range of 1 to 1000 ng/ml and 2.5 to 1000 ng/ml for I and II, respectively.

Estrogen receptor-binding affinity of tamoxifen analogs with various side chains and their biologic profile in immature rat uterus

Estrogen receptor-binding affinity and estrogenic and antiestrogenic activity have been evaluated for tamoxifen analogs substituted with various side chains. Antagonist activity of the compounds of this series appears to be dependent on the presence of the beta-tert-aminoethoxy moiety. The results also indicate that the dissociation of these compounds from the estrogen receptor-binding site at 25 C is very slow.

A chemical classification of nonsteroidal antagonists of sex-steroid hormone action

A highly varied collection of nonsteroids have been reported over the last forty years as being able to exert an antihormonal action versus steroid hormones in vivo. This diversity is partly explained by the manifold molecular targets of these compounds which may be either enzymes or receptors (leading to inhibition of steroid production and action respectively) and by the different possible levels of interference within feedback loops between the central nervous system, pituitary, gonads and other peripheral organs. The present chapter is a chemist's classification of some of these structures often in the absence of detailed biochemical data. Nonsteroid antiestrogens (and estrogens) most often share a common feature with diethylstilbestrol and consequently the effects of structural modifications on biological activities can be studied in a rational manner. This is not the case for non-steroidal antiandrogens that we have only been able to classify into conventional chemical groups. Nor have any true lead compounds nor well-defined chemical classes been identified for nonsteroid antiprogestogens. This is however the only hormonal class where natural products play an important role.

Enhanced antifertility activity of non-steroidal molecules with 3-n-butylamino-2-hydroxypropyloxy side chain

A comparative study of relative binding affinity (RBA) for estradiol-17 beta-receptors, estrogenicity and antifertility activity of compounds 2,2-dimethyl-3-phenyl-4-p-(3-n-butylamino-2-hydroxypropyloxy-pheny l)- 7-methoxycoumarin 4, 2,2-dimethyl-3-phenyl-4-p-(3-n-butylamino-2-hydroxy-propyloxyphenyl++ +)-7-methoxy chromene 5 and trans-2,2-dimethyl-3-phenyl-4-p-(3-n-butylamino-2-hydroxypropyloxyphe nyl)- 7-methoxychroman 6 with the corresponding 4-p-(beta-pyrrolidinoethoxyphenyl) compounds 1-3, is reported. It has been found that the introduction of the novel 3-n-butylamino-2-hydroxypropyloxy moiety in place of the classical tert-beta-aminoethoxy group leads to enhancement of antifertility activity.