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The application of parallel synthesis to lead optimization programs in drug discovery has been an ongoing challenge since the first reports of library synthesis. A number of approaches to the application of parallel array synthesis to lead optimization have been attempted over the years, ranging from widespread deployment by (and support of) individual medicinal chemists to centralization as a service by an expert core team. This manuscript describes our experience with the latter approach, which was undertaken as part of a larger initiative to optimize drug discovery. In particular, we highlight how concepts taken from the manufacturing sector can be applied to drug discovery and parallel synthesis to improve the timeliness and thus the impact of arrays on drug discovery.

A structure-activity study of the dual acting ACE/NEP inhibitors related to 1a and 1b was undertaken to determine the parameters critical for activity versus ACE and NEP in vitro.

Mercaptoacyl dipeptides were prepared as dual-acting ACE/NEP inhibitors. Inhibition of each enzyme may be explained by different binding models. Structure-activity studies determined that, in this series of compounds, the mercaptopropanoyl dipeptide framework leads to increased affinity for NEP but diminished ACE activity in vivo .

A series of benzo-fused lactams were incorporated as conformationally restricted dipeptide mimetics of Ala-Pro in dual-acting ACE/NEP inhibitors 1 and 2. The result of this modification led to compounds possessing excellent inhibitory potency versus ACE and NEP both in vitro and in vivo.

Prodrug derivatization of a potent quinoline-4-carboxylic acid angiotensin II receptor antagonist was Undertaken as an approach to achieve improved oral activity. A dioxolenone carboxylic ester and an alkylated tetrazole prodrug both showed greater oral antihypertensive acivity in the salt-deplete spontaneously hypertensive rat and increased oral bioavailability relative to the parent compound.

The syntheses and pharmacological activity of a series of 1,4-substituted indoles which function as nonpeptidic antagonists of the angiotensin II (AII) receptor are described. Compounds in this series are orally active and demonstrate long lasting antihypertensive activity.

The syntheses and pharmacological activity of a series of diol sulfonamides which function as inhibitors of human renin are described. The most potent compound in this series, compound 20 (SQ 33,800 ), is a subnanomolar inhibitor of human renin (IC 50 = 0.35 × 10 −9 M).

In order to identify potential cytochrome P-450 3A4 (drug-metabolizing enzyme) inducers at an early stage of the drug discovery process, a cell-based transactivation high-throughput luciferase reporter assay for the human pregnane X receptor (PXR) in HepG2 cells has been implemented and multiplexed with a viability end point for data interpretation, as part of a Lead Profiling portfolio of assays. As a routine part of Lead Profiling operations, assays are periodically evaluated for utility as well as for potential improvements in technology or process. We used a recent evaluation of our PXR-transactivation assay as a model for the application of Lean Thinking-based process analysis to lab-bench assay optimization and automation. This resulted in the development of a 384-well multiplexed homogeneous assay simultaneously detecting PXR transactivation and HepG2 cell cytotoxicity. In order to multiplex fluorescent and luminescent read-outs, modifications to each assay were necessary, which included optimization of multiple assay parameters such as cell density, plate type, and reagent concentrations. Subsequently, a set of compounds including known cytotoxic compounds and PXR inducers were used to validate the multiplexed assay. Results from the multiplexed assay correlate well with those from the singleplexed assay formats measuring PXR transactivation and viability separately. Implementation of the multiplexed assay for routine compound profiling provides improved data quality, sample conservation, cost savings, and resource efficiencies.

Fosinopril is an acyloxyalkyl ester of fosinoprilat, a phosphinic acid angiotensin-converting enzyme (ACE) inhibitor developed for the treatment of hypertension and congestive heart failure. The hydroxylphosphinylacetyl proline class of inhibitors exhibits high affinity for ACE and a high degree of efficacy for inhibition of the angiotensin I-induced pressor response in animals (Krapcho et al., 1988) when administered intravenously. These inhibitors exhibited a low level of activity upon oral administration, which could be attributed to low oral absorption. The propanoyloxy isobutyl ester of the trans-4-cyclohexyl proline analog exhibited improved oral activity and long duration of action (DeForrest et al., 1989) and was advanced into preclinical and clinical development (Duchin, 1991).

The design and application of α-hydroxy phosphonates, a new class of transition state analogs, toward the discovery of novel and potent inhibitors of the aspartyl protease renin is described. Tripeptidic α-hydroxy diethyl phosphonate 3, the first example in this series, was found to be a good inhibitor of human renin (IC 50 = 29 nM), and preliminary studies led to the choice of α-hydroxy dimethyl phosphonate 15 (IC 50 = 16 nM) as a base-line compound for further structure-activity relationship study. Corresponding phosphinate (28-30) and phosphine oxide (23 and 24) analogs of 15 were prepared to assess the steric and electronic requirements around the phosphorus center. Evaluation of these analogs suggested that the presence of at least one alkoxy group on phosphorus was a critical requirement for good activity. Inhibitors with leucine at P 2 possessed better in vitro activity than the corresponding P 2 histidine analogs (15, IC 50 = 16 nM vs 37, IC 50 = 220 nM ; 33, IC 50 = 8.5 nM vs 40, IC 50 = 41 nM). Compound 34 (IC 50 = 31 nM), the P 3 aminocaproic analog of 15, showed complete and long-lasting inhibition of plasma renin activity while eliciting a 10-15 mmHg drop in mean arterial pressure when administered intravenously at 1 μmol/kg in conscious, sodium-depleted, cynomolgus monkeys. In summary, the α-hydroxy phosphonates represent a promising and structurally novel class of transition state analog inhibitors of human renin.

Application of the concept of activated ketones to the design of novel and potent transition-state analog inhibitors of the aspartyl protease renin is described. Three different classes of peptidic activated ketones were synthesized: 1,1,1-trifluoromethyl ketones, alpha-keto esters, and alpha-diketones. The corresponding alcohols were also evaluated as renin inhibitors in each series. While the trifluoromethyl alcohol 12 (I50 = 4000 nM) was equipotent to the simple methyl alcohol 7 (I50 = 3200 nM), the structurally similar alpha-hydroxy esters (32 and 30, I50's = 5.3 and 4.7 nM, respectively) and alpha-hydroxy ketones (41 and 42, I50 = 23 and 15 nM, respectively) were 150-300-fold more active. The hydrating capability of the activated ketone functionality was important for intrinsic potency in the case of trifluoromethyl ketones, as illustrated by the significantly better activity of trifluoromethyl ketone 13 (I50 = 250 nM) compared to its alcohol analog 12 (I50 = 4000 nM). It was however unimportant for the alpha-keto ester (20 and 31, I50 = 15 and 4.1 nM, respectively) and alpha-diketone (43 and 44, I50 = 52 and 28 nM, respectively) based inhibitors, since their activity was essentially similar to that of the corresponding alcohols. These results collectively suggest that, whereas the trifluoromethyl ketones derive their renin inhibitory potency primarily from their ability to become hydrated, this is not a critical feature for the activity of alpha-dicarbonyl-based inhibitors. The alpha-keto ester and alpha-diketone based renin inhibitors benefit predominantly from the hydrophobic and/or H-bonding type binding interactions of the neighboring ester or acyl group itself, rather than the ability of this group to deactivate the adjacent ketone group and thereby make it susceptible to hydration.

Analogues of (S)-1-[6-amino-2[[hydroxy(4-phenylbutyl)phosphinyl] oxy]-1-oxohexyl]-L-proline (1, SQ 29,852) in which the terminal proline residue has been replaced by a variety of substituted and heteroatom-substituted prolines, N-arylglycines, N-cycloalkylglycines, and bicyclic amino acids have been synthesized and evaluated as inhibitors of angiotensin converting enzyme in vitro and in vivo. In general, the addition of lipophilic substituents to the 4-position of proline of the parent phosphonate 1 resulted in substantial increases in in vitro activity. The largest improvements were observed in the case of cis-benzyl (36-fold) and dithioketal (24-fold) analogues 2r and 2x, respectively. These enhancements of in vitro activity were accompanied by modest increases (2-3.5-fold) in in vivo (iv) activity. Among the various terminal amino acid replacements examined in this study, the indoline-based analogue 2i was by far the most potent compound on iv administration in the normotensive rat.

A decade of experimentation, with work in the last four years greatly accelerated by the availability of captopril, favors the conclusion that angiotensin-converting enzyme inhibitors exert their antihypertensive effect by blocking the formation of angiotensin II. The apparently anomalous efficacy of ACE inhibitors in hypertension characterized by low circulating renin levels may point to the importance of the vascular renin-angiotensin system in controlling blood pressure. Neither kinin potentiation nor blockade of the CNS renin-angiotensin system appear to play a significant role in the antihypertensive effect of captopril. Pharmacological and clinical studies on ACE inhibitors of novel chemical structure will establish their utility as antihypertensive agents and may lead to greater understanding of the mechanism of action of all ACE inhibitors.

The synthesis of a series of orally active, phosphinyloxyacyl proline inhibitors of angiotensin converting enzyme (ACE) is described. The in vitro and in vivo ACE inhibitory activities are reported for each compound. The structure-activity relationship for this series of compounds in relation to the carboxyalkyl dipeptide ACE inhibitors as well as other types of hydroxyphosphinyl-containing ACE inhibitors (e.g., the corresponding nitrogen and carbon isosteres) is discussed. Within an isosteric series of phosphorus-containing inhibitors based on the lysylproline terminal dipeptide sequence, only the phosphonates (oxygen isosteres) show a high level of oral activity. Optimum potency and oral activity in the phosphonate series occurs with the (phenylbutyl)- and n-hexylphosphonate side chains. An aminobutyl side chain in the P1' residue is an absolute requirement for full expression of oral activity. The most potent of these compounds, 8b (SQ 29,852), has intravenous and oral activities superior in potency to those of captopril in the normotensive rat.

A series of mercaptoacyl amino acids and related compounds was synthesized and evaluated for inhibition of angiotensin-converting enzyme (ACE) in order to determine the nature and importance of the putative interaction between ACE and the amide moiety of inhibitors such as captopril (3-mercapto-2-methylpropanoyl-L-proline). It was concluded that the interaction involves a hydrogen bond from a donor site on ACE to the oxygen of the amide carbonyl. Compounds in which the amide moiety is replaced by other groups (ester, ketone, sulfonamide) capable of accepting a hydrogen bond are effective inhibitors, but compounds in which only the geometrical features of the amide are retained are ineffective inhibitors. The presence of an NH group is not necessary for effective inhibition. The activity of a series of mercaptoacyl cycloalkyl carboxylic acids parallels the activity of the isosteric series of mercaptoacyl imino acids.

The title compound was synthesized via its diethyl ester from 1-pyrroline trimer and diethyl phosphite. The 3-mercaptopropanoyl derivative inhibited angiotensin converting enzyme with I 50 = 1.7 μM.