Michael Francis Rafferty

No Denying It: Medicinal Chemistry Training Is in Big Trouble

There has been little consensus between the pharmaceutical industry and academic communities concerning the best approach to train medicinal chemists for drug discovery. For decades the pharmaceutical industry has shown preference for synthetic organic graduates over candidates with degrees from medicinal chemistry programs on the assumption that medicinal chemistry expertise will be acquired on the job. However, ongoing changes to pharmaceutical drug discovery organizations and practices threaten to undermine this training model. There is a compelling argument to be made for establishment of a strong industry-academic partnership to train new candidates with sophisticated knowledge of contemporary drug design concepts and techniques to ensure that the future needs of both industry and academic drug discovery research can be served.

Gas chromatographic quantitation of underivatized amines in the determination of their octanol-0.1 M sodium hydroxide partition coefficients by the shake-flask method.

The use of gas chromatography (GC) for the determination of 0.1 M sodium hydroxide-octanol partition coefficients (log P) for a wide variety of ethylamines is demonstrated. The conventional shake-flask procedure (SFP) is utilized, with the addition of an internal reference, which is cleanly separated from the desired solute and solvents on a 10% Apiezon L, 2% potassium hydroxide on 80-100 mesh Chromosorb W AW column. The partitioned solute is extracted from the aqueous phase with chloroform and analyzed by GC. The method provides an accurate and highly reproducible means of determining log P values, as demonstrated by the low relative standard errors. The technique is both rapid and extremely versatile. The use of the internal standard method of analysis introduces consistency, since variables like the exact weight of solute are not necessary (unlike the traditional SFP) and the volume of sample injected is not critical. The technique is readily accessible to microgram quantities of solutes, making it ideal for a wide range of volatile, amine-bearing compounds.

Conformational preferences of dopamine analogues for inhibition of norepinephrine N-methyltransferase. Conformationally defined adrenergic agents. 7☆

A series of analogues of dopamine (DA) with varying degrees of conformational flexibility have been examined as potential substrates or competitive inhibitors of the enzyme norepinephrine N-methyltransferase (NMT). A conformationally defined (rigid) analogue of the fully extended conformation of DA, 2-amino-6,7-dihydroxybenzonorbornene hydrobromide (3; 6,7-D2HX) proved to be a better substrate than the non-catechol parent 2-aminobenzonorbornene (4; 2HX). However, analogues 3 and 4 displayed equivalent competitive inhibitory activity toward phenylethanolamine (PEA). Neither 6,7-ADTN (5), a DA analogue in the 2-aminotetralin (2AT) system, nor 6,7-DTHIQ (7), a DA analogue in the tetrahydroisoquinoline (THIQ) system, showed substrate activity; 6,7-ADTN was a poorer competitive inhibitor than the parent 2AT but 6,7-DTHIQ was a better competitive inhibitor than its parent, THIQ (8). A tricyclic conformationally defined analogue 9 of 6,7-ADTN was devoid of either substrate or inhibitory activity. From these results it may be concluded that a fully extended side chain conformation is required for NMT substrate activity, and the better substrate activity for 6,7-D2HX compared to 4 is consistent with a proper catechol orientation for interaction with the norepinephrine (NE) binding site of NMT.

Conformational aspects of binding of substrates and inhibitors of phenylethanolamine N-methyltransferase (PNMT)

Recently, we reported the results of an investigation into the conformational requirements for binding of phenylethylamine inhibitors to phenylethanolamine N-methyltransferase (PNMT; E.C. 2.1.1.28) using a series of conformationally-defined phenylethylamine analogues (Grunewald et al., 1981). The conclusions of this study were that PNMT would accept only a fully extended side chain conformation and that folded (gauche) conformations of phenylethylamine could not bind to the active site. We have now completed the synthesis of several trifluoromethyl-substituted derivatives of two of the compounds from this study (exo- and endo-2-aminobenzobicyclo[2.2.1]heptene, compounds 1 and6) and, since Fuller et al. (1971; 1972) have demonstrated that the addition of polar, lipophilic substituents to the aromatic ring of phenylethylamines greatly enhances affinity for the active site, we examined these new derivatives for PNMT activity. Compounds 1-5 are analogues of a fully extended conformation of phenylethylamine, and based on the activity found for 1 in the previous study, were expected to be competitive inhibitors of the enzyme; compound 6 was found previously to be a weak uncompetitive inhibitor of PNMT and so the substituted derivatives 7–9 were expected to behave similarly.

Stereochemical aspects of binding of aromatic and non-aromatic substrates and inhibitors to phenylethanolamine N-methyltransferase

Phenylethanolamine N-methyltransferase (PNMT; E.C.2.1.1.28) catalyzes the final step in the epinephrine biosynthetic pathway, that being the methylation of norepinephrine using S-adenosyl-L-methionine (SAM) as the methyl donor (Axelrod, 1962). PNMT occurs mainly in the adrenal medulla, but has also been reported in areas of the central nervous system, specifically regions of the hypothalamus and brainstem (Saavedra et al., 1974; Hokfelt et al., 1974). Evidence that PNMT activity in specific regions of the brainstem and hypothalamus increases with developing hypertension (Saavedra et al., 1976; Saavedra et al., 1978; Petty and Reid, 1979) has stimulated interest in the development of specific inhibitors of PNMT as potential tools for determining the role of these epinephrine-containing neurons in the CNS (Davis et al., 1980; Fuller et al., 1978; Pendleton et al., 1976; Fuller, 1979; and references cited therein).