Design and evaluation of a series of pyrazolopyrimidines as p70S6K inhibitors.

The 70-kDa ribosomal protein S6 kinase (p70S6K) is part of the PI3K/AKT/mTOR pathway and has been implicated in cancer. High throughput screening versus p70S6K led to the identification of aminopyrimidine 3a as active inhibitor. Lead optimization of 3a resulted in highly potent, selective, and orally bioavailable pyrazolopyrimidines. In this manuscript we report the structure-activity relationship of this series and pharmacokinetic, pharmacodynamic, and efficacy data of the lead compound 13c.

Pyrazolopyrimidines as dual Akt/p70S6K inhibitors.

Activation of the PI3K/Akt/mTOR kinase pathway is frequently associated with human cancer. Selective inhibition of p70S6Kinase, which is the last kinase in the PI3K pathway, is not sufficient for strong tumor growth inhibition and can lead to activation of upstream proteins including Akt through relief of a negative feedback loop. Targeting multiple sites in the PI3K pathway might be beneficial for optimal activity. In this manuscript we report the design of dual Akt/p70S6K inhibitors and the evaluation of the lead compound 11b in vivo, which was eventually advanced into clinical development.

Discovery of XL888: a novel tropane-derived small molecule inhibitor of HSP90.

With structural guidance, tropane-derived HTS hits were modified to optimize for HSP90 inhibition and a desirable in vivo profile. Through an iterative SAR development process 12i (XL888) was discovered and shown to reduce HSP90 client protein content in PD studies. Furthermore, efficacy experiments performed in a NCI-N87 mouse xenograft model demonstrated tumor regression in some dosing regimens.

Determination of the Absolute Stereochemistry of (-)-Galbonolide A.

The absolute stereochemistry of (-)-galbonolide A (1) was assigned by chemical methods. First, 1 was degraded to diol 3. After selective silylation of the primary alcohol, two independent methods were carried out to determine the chirality at C13. Both established its S-configuration. Using the methodology developed in the total synthesis of (-)-galbonolide B, diols 13(S,S) and 13(S,R) were prepared. Their (R)-MTPA esters, 14(S,S,R) and 14(S,R,R), were compared with the analogous (R)-MTPA ester of the degradation product 3, which subsequently established the S-chirality at C8. To determine the chirality at C4, two independent methods were carried out. One involved a comparison with the chirality of C4 of galbonolide B. The other involved a comparison of the degradation product of galbonolide A, 22, with its synthetic equivalents. Both methods confirmed the S-configuration at C4. Since three of the four chiral centers of galbonolides A and B have been confirmed to be identical and since the two galbonolides share very similar conformations as suggested by their (1)H NMR spectra, the configurations at C2 of these two compounds should also be the same.

Discovery of a novel class of highly potent, selective, ATP-competitive, and orally bioavailable inhibitors of the mammalian target of rapamycin (mTOR).

A series of novel, highly potent, selective, and ATP-competitive mammalian target of rapamycin (mTOR) inhibitors based on a benzoxazepine scaffold have been identified. Lead optimization resulted in the discovery of inhibitors with low nanomolar activity and greater than 1000-fold selectivity over the closely related PI3K kinases. Compound 28 (XL388) inhibited cellular phosphorylation of mTOR complex 1 (p-p70S6K, pS6, and p-4E-BP1) and mTOR complex 2 (pAKT (S473)) substrates. Furthermore, this compound displayed good pharmacokinetics and oral exposure in multiple species with moderate bioavailability. Oral administration of compound 28 to athymic nude mice implanted with human tumor xenografts afforded significant and dose-dependent antitumor activity.

Novel Carboxamide-Based Allosteric MEK Inhibitors: Discovery and Optimization Efforts toward XL518 (GDC-0973).

The ERK/MAP kinase cascade is a key mechanism subject to dysregulation in cancer and is constitutively activated or highly upregulated in many tumor types. Mutations associated with upstream pathway components RAS and Raf occur frequently and contribute to the oncogenic phenotype through activation of MEK and then ERK. Inhibitors of MEK have been shown to effectively block upregulated ERK/MAPK signaling in a range of cancer cell lines and have further demonstrated early evidence of efficacy in the clinic for the treatment of cancer. Guided by structural insight, a strategy aimed at the identification of an optimal diphenylamine-based MEK inhibitor with an improved metabolism and safety profile versus PD-0325901 led to the discovery of development candidate 1-({3,4-difluoro-2-[(2-fluoro-4-iodophenyl)amino]phenyl}carbonyl)-3-[(2S)-piperidin-2-yl]azetidin-3-ol (XL518, GDC-0973) (1). XL518 exhibits robust in vitro and in vivo potency and efficacy in preclinical models with sustained duration of action and is currently in early stage clinical trials.

Regiochemistry in 1,3-dipolar cycloadditions of the azomethine ylide formed from diethyl aminomalonate and paraformaldehyde.

The azomethine ylide derived from the condensation of diethyl aminomalonate with paraformaldehyde undergoes 1,3-dipolar cycloadditions with acrylate and propiolate derivatives. Contrary to a previous report, these reactions yield mixtures of regioisomers generally favoring the 2,2,3-trisubstituted product. However, the relative quantity of the 2,2,4-trisubstituted product formed increases with an increase in the size of the activating group on the dipolaroplile.