Joel Robichaud

The discovery of odanacatib (MK-0822), a selective inhibitor of cathepsin K.

Odanacatib is a potent, selective, and neutral cathepsin K inhibitor which was developed to address the metabolic liabilities of the Cat K inhibitor L-873724. Substituting P1 and modifying the P2 side chain led to a metabolically robust inhibitor with a long half-life in preclinical species. Odanacatib was more selective in whole cell assays than the published Cat K inhibitors balicatib and relacatib. Evaluation in dermal fibroblast culture showed minimal intracellular collagen accumulation relative to less selective Cat K inhibitors.

Trifluoroethylamines as amide isosteres in inhibitors of cathepsin K

The P2-P3 amide of dipeptide cathepsin K inhibitors can be replaced by the metabolically stable trifluoroethylamine group. The non-basic nature of the nitrogen allows the important hydrogen bond to Gly66 to be made. The resulting compounds are 10- to 20-fold more potent than the corresponding amide derivatives. Compound 8 is a 5 pM inhibitor of human cathepsin K with >10,000-fold selectivity over other cathepsins.

TOTAL SYNTHESIS OF (+)-DYSIDIOLIDE

Dysidiolide (1 or ent-1), a novel sesterterpenoid isolated in 1996 from the Caribbean sponge Dysidea etheria de Laubenfels, exhibits antitumor activity at the micromolar level, and most importantly, it is the first natural product discovered thus far to inhibit protein phosphatase cdc25A (IC50 ) 9.4 μM).1 In addition to such remarkable biological properties, which may have utility in the treatment of cancer,1,2 dysidiolide also possesses a unique carbon skeleton with structural features that find no precedent in nature. Central to the molecular array is the close proximity of the two side chains (ca. 4 A apart) and the γ-hydroxylbutenolide residue, which is believed to serve as a surrogate phosphate when the molecule is bound to cdc25A.1 While the structure and relative stereochemistry of dysidiolide were determined by single-crystal X-ray analysis, its absolute configuration was not assigned.1,3 We report here the first total synthesis of 1 that establishes the absolute stereostructure of natural dysidiolide as ent-1 and provides the basis for producing a range of designed analogues for SAR studies. Our synthetic strategy (Scheme 1) entailed elaboration of 1 by addition of [(triisopropylsilyl)oxy]furan reagent A (M ) Li or TiX3) to aldehyde 2 and subsequent oxyfunctionalization of the furan ring by utilizing methodology developed in this laboratory.4 The preferred conformer5 of 2 (shown in Scheme 1) would undergo attack from the least hindered re-face of the carbonyl group, thereby setting the required S-stereochemistry at C-4. Convergent construction of the decalin framework was envisioned by Diels-Alder reaction of chiral diene 5 with the doubly activated dienophile 6. Previous findings with similar dienophiles6 suggested that both the regioselectivity and endo/exo selectivity should proceed as planned. Inspection of molecular models further suggested that the desired π-facial selectivity would be dictated by the preferred conformation of diene 5 (cf. Scheme 1), which minimizes A1,2-strain.7 Thus, all chirality in 1 would derive from the single stereocenter in 5. Diene 5 was prepared from methyl (R)-(+)-1-methyl-2oxocyclohexanepropionate (7, ca. 90% ee)8 by reduction to the corresponding diol,9 selective benzylation of the primary alcohol, TPAP-oxidation,10 addition of vinylcerium dichloride11 and dehydration of the resulting allylic alcohol by heating in the presence of CuSO4 (Scheme 2). The overall yield of this five-step sequence was 64.6%.12 Access to dienophile 6was gained in a fully stereoselective manner by ethoxycarbonylation of acetylene13 9, conjugate addition of in situ generated lithium divinylcuprate,14 and ozonolysis of the vinyl group15 (Scheme 3). With 5 and 6 in hand, we turned to the crucial DielsAlder reaction, which proved especially serviceable under mediation by ethylaluminum dichloride in CH2Cl2 at -94 °C (Scheme 4). Under these conditions, only two of the eight possible adducts were produced (4 and 12) in a ratio of 2.3:1 (76% yield). Reduction of the so-obtained 4/12mixture with LiEt3BH provided the easily separable diols16 13 and 14 in yields of 43 and 18%, respectively (over two steps). In keeping with our plan, elaboration of diol 13 to intermediate 3 next required deoxygenation of the vicinal hydroxymethyl substituents (Scheme 5). This and the ensuing step, which entailed removal of the benzyl protecting (1) Gunasekera, S. P.; McCarthy, P. J.; Kelly-Borges, M.; Lobkovsky, E.; Clardy, J. J. Am. Chem. Soc. 1996, 118, 8759. (2) Millar, J. B. A.; Russell, P. Cell 1992, 68, 407. (3) Structural elucidation by NMR was particularly difficult due to the presence of both lactol epimers in solution and/or the hindered motions of the lactol ring (ref 1). (4) Boukouvalas, J.; Lachance. N. Synlett 1998, in press. (5) Molecular mechanics calculations using CHARMm forcefield quanta simulation software indicated that this conformer corresponds to the lowest energy minimum and is favored by at least 1.1 kcal/mol over those susceptible to undergo si-face attack. We thank Professor Josee Brisson for invaluable assistance. (6) Corey, E. J.; Desai, M. C. Tetrahedron Lett. 1985, 26, 5747. Kakushima, M.; Espinosa, J.; Valenta, Z. Can. J. Chem. 1976, 54, 3304. (7) Johnson, F. Chem. Rev. (Washington, D.C.) 1968, 68, 375. (8) Ketone 7 and its antipode are commercially available or easily prepared on a large scale from racemic 2-methylcyclohexanone by d’Angelo’s two-step procedure: d’Angelo, J.; Desmaele, D.; Dumas, F.; Guingant, A. Tetrahedron: Asymmetry 1992, 3, 459. (9) Tori, M.; Kosaka, K.; Asakawa, Y. J. Chem. Soc., Perkin Trans. 1 1994, 2039. (10) Ley, S. V.; Norman J.; Griffith, W. P.; Marsden, S. P. Synthesis 1994, 639. (11) The use of freshly dried CeCl3 was essential for optimal results; see also: Ladouceur, G.; Paquette, L. A. Synthesis 1992, 185. Dimitrov, V.; Kostova, K.; Genov, M. Tetrahedron Lett. 1996, 37, 6787. (12) Yields refer to chromatographically and spectroscopically homogeneous products. All new compounds exhibited satisfactory elemental analyses and/or exact mass data. (13) Lipshutz, B. H.; Wood, M. R. J. Am. Chem. Soc. 1993, 115, 12625. (14) Keck, G. A.; Nickell, D. G. J. Am. Chem. Soc. 1980, 102, 3632. Krause, N. Tetrahedron Lett. 1989, 30, 5219. (15) Stotter, P. L.; Eppner, J. B. Tetrahedron Lett. 1973, 2417. (16) The structural assignments to these diols follow from NOE studies. Details of these experiments will be provided in the full paper. Scheme 1

Biological activity and preclinical efficacy of azetidinyl pyridazines as potent systemically-distributed stearoyl-CoA desaturase inhibitors

Potent and orally bioavailable SCD inhibitors built on an azetidinyl pyridazine scaffold were identified. In a one-month gDIO mouse model of obesity, we demonstrated that there was no therapeutic index even at low doses; efficacy in preventing weight gain tracked closely with skin and eye adverse events. This was attributed to the local SCD inhibition in these tissues as a consequence of the broad tissue distribution observed in mice for this class of compounds. The search for new structural scaffolds which may display a different tissue distribution was initiated. In preparation for an HTS campaign, a radiolabeled azetidinyl pyridazine displaying low non-specific binding in the scintillation proximity assay was prepared.

The discovery of MK-0674, an orally bioavailable cathepsin K inhibitor

MK-0674 is a potent and selective cathepsin K inhibitor from the same structural class as odanacatib with a comparable inhibitory potency profile against Cat K. It is orally bioavailable and exhibits long half-life in pre-clinical species. In vivo studies using deuterated MK-0674 show stereoselective epimerization of the alcohol stereocenter via an oxidation/reduction cycle. From in vitro incubations, two metabolites could be identified: the hydroxyleucine and the glucuronide conjugate which were confirmed using authentic synthetic standards.

Applying the pro-drug approach to afford highly bioavailable antagonists of P2Y14

Our series of competitive antagonists against the G-protein coupled receptor P2Y(14) were found to be highly shifted in the presence of serum (>99% protein bound). A binding assay using 2% human serum albumin (HSA) was developed to guide further SAR studies and led to the identification of the zwitterion 2, which is substantially less shifted (18-fold) than our previous lead compound 1 (323-fold). However, as the bioavailability of 2 was low, a library of ester pro-drugs was prepared (7a-7j) and assessed in vitro. The most interesting candidates were then profiled in vivo and led to the identification of the pro-drug 7j, which possesses a substantially improved pharmacokinetic profile.

The identification of 4,7-disubstituted naphthoic acid derivatives as UDP-competitive antagonists of P2Y14.

A weak, UDP-competitive antagonist of the pyrimidinergic receptor P2RY(14) with a naphthoic acid core was identified through high-throughput screening. Optimization provided compounds with improved potency but poor pharmacokinetics. Acylglucuronidation was determined to be the major route of metabolism. Increasing the electron-withdrawing nature of the substituents markedly reduced glucuronidation and improved the pharmacokinetic profile. Additional optimization led to the identification of compound 38 which is an 8 nM UDP-competitive antagonist of P2Y(14) with a good pharmacokinetic profile.

Bicyclic heteroaryl inhibitors of stearoyl-CoA desaturase: From systemic to liver-targeting inhibitors

Optimization of a lead thiazole amide MF-152 led to the identification of potent bicyclic heteroaryl SCD1 inhibitors with good mouse pharmacokinetic profiles. In a view to target the liver for efficacy and to avoid SCD1 inhibition in the skin and eyes where adverse effects were previously observed in rodents, representative systemically-distributed SCD1 inhibitors were converted into liver-targeting SCD1 inhibitors.

Investigation of ketone warheads as alternatives to the nitrile for preparation of potent and selective cathepsin K inhibitors

Amino ketone warheads were explored as alternatives to the nitrile group of a potent and selective cathepsin K inhibitor. The resulting compounds were potent and selective inhibitors of cathepsin K and these nitrile replacements had a significant effect on metabolism and pharmacokinetics.

Photo-crosslinking of proteins in intact cells reveals a dimeric structure of cyclooxygenase-2 and an inhibitor-sensitive oligomeric structure of microsomal prostaglandin E2 synthase-1

We have characterized the structures of cyclooxygenase-2 (COX-2) and microsomal prostaglandin E(2) synthase-1 (mPGES-1) in intact cells using bifunctional and photo-activatable crosslinking agents. A dimeric complex was detected for COX-2 by both crosslinking approaches, consistent with the crystal structure of the enzyme. For mPGES-1, treatment of A549 cells with disuccinimidyl suberate yielded immunoreactive protein bands corresponding to a dimer (33 kDa) and a trimer (45 kDa), as observed for the isolated enzyme. Photo-crosslinking with photoactivatable methionine in intact cells generated complexes with molecular weights corresponding to the dimer (33 kDa) and two putative trimer forms (50 and 55 kDa). Treatment with the selective mPGES-1 inhibitor MF63 prevented the formation of the 50 and 55 kDa crosslinked complexes, while an inactive structural analogue had no effect. Our data indicate that COX-2 forms a dimer in intact cells and that mPGES-1 has an oligomeric structure that can be disrupted by a selective inhibitor.