Design of a brain-penetrant CDK4/6 inhibitor for glioblastoma.

CDK4 and CDK6 are kinases with similar sequences that regulate cell cycle progression and are validated targets in the treatment of cancer. Glioblastoma is characterized by a high frequency of CDKN2A/CCND2/CDK4/CDK6 pathway dysregulation, making dual inhibition of CDK4 and CDK6 an attractive therapeutic approach for this disease. Abemaciclib, ribociclib, and palbociclib are approved CDK4/6 inhibitors for the treatment of HR+/HER2- breast cancer, but these drugs are not expected to show strong activity in brain tumors due to poor blood brain barrier penetration. Herein, we report the identification of a brain-penetrant CDK4/6 inhibitor derived from a literature molecule with low molecular weight and topological polar surface area (MW = 285 and TPSA = 66 Å2), but lacking the CDK2/1 selectivity profile due to the absence of a basic amine. Removal of a hydrogen bond donor via cyclization of the pyrazole allowed for the introduction of basic and semi-basic amines, while maintaining in many cases efflux ratios reasonable for a CNS program. Ultimately, a basic spiroazetidine (cpKa = 8.8) was identified that afforded acceptable selectivity over anti-target CDK1 while maintaining brain-penetration in vivo (mouse Kp,uu = 0.20-0.59). To probe the potency and selectivity, our lead compound was evaluated in a panel of glioblastoma cell lines. Potency comparable to abemaciclib was observed in Rb-wild type lines U87MG, DBTRG-05MG, A172, and T98G, while Rb-deficient cell lines SF539 and M059J exhibited a lack of sensitivity.

Substrate-Controlled Diastereoselectivity Reversal in NHC-Catalyzed Cross-Benzoin Reactions Using N-Boc-N-Bn-Protected α-Amino Aldehydes.

The effectiveness of utilizing N-Bn-N-Boc-α-amino aldehydes in cross-benzoin reactions with heteroaromatic aldehydes is demonstrated. The reaction is both chemoselective and syn-selective, making it complementary to the anti-selective cross-benzoin reaction of NHBoc-α-amino aldehydes. Good diastereoselectivity is obtained for a variety of amino aldehydes, including nonhindered ones. A Felkin-Anh model can be used to rationalize the observed diastereoselectivity.

Optimization of a Novel DEL Hit That Binds in the Cbl-b SH2 Domain and Blocks Substrate Binding.

We were attracted to the therapeutic potential of inhibiting Casitas B-lineage lymphoma proto-oncogene-b (Cbl-b), a RING E3 ligase that plays a critical role in regulating the activation of T cells. However, given that only protein-protein interactions were involved, it was unclear whether inhibition by a small molecule would be a viable approach. After screening an ∼6 billion member DNA-encoded library (DEL) using activated Cbl-b, we identified compound 1 as a hit for which the cis-isomer (2) was confirmed by biochemical and surface plasmon resonance (SPR) assays. Our hit optimization effort was greatly accelerated when we obtained a cocrystal structure of 2 with Cbl-b, which demonstrated induced binding at the substrate binding site, namely, the Src homology-2 (SH2) domain. This was quite noteworthy given that there are few reports of small molecule inhibitors that bind to SH2 domains and block protein-protein interactions. Structure- and property-guided optimization led to compound 27, which demonstrated measurable cell activity, albeit only at high concentrations.

Discovery of Selective Tertiary Amide Inhibitors of Cyclin-Dependent Kinase 2 (CDK2).

Cyclin-dependent kinases (CDKs) are key regulators of the cell cycle and are frequently altered in cancer cells, thereby leading to uncontrolled proliferation. In this context, CDK2 has emerged as an appealing target for anticancer drug development. Herein, we describe the discovery of a series of selective small molecule inhibitors of CDK2 beginning with historical compounds from our ERK2 program (e.g., compound 6). Structure-based drug design led to the potent and selective tool compound 32, where excellent selectivity against ERK2 and CDK4 was achieved by filling the lipophilic DFG-1 pocket and targeting interactions with CDK2-specific lower hinge binding residues, respectively. Compound 32 demonstrated 112% tumor growth inhibition in mice bearing OVCAR3 tumors with 50 mg/kg bis in die (BID) oral dosing.

Total Synthesis of (+)-Hyacinthacine A1 Using a Chemoselective Cross-Benzoin Reaction and a Furan Photooxygenation-Amine Cyclization Strategy.

We report the shortest synthesis of glycosidase inhibitor (+)-hyacinthacine A1 using a highly chemoselective N-heterocyclic carbene-catalyzed cross-benzoin reaction as well as a furan photooxygenation-amine cyclization strategy. This is the first such cyclization on a furylic alcohol, an unprecedented reaction due to the notorious instability of the formed intermediates. The photooxygenation strategy was eventually incorporated into a three-step one-pot process that formed the requisite pyrrolizidine framework of (+)-hyacinthacine A1.

Chemo- and Diastereoselective N-Heterocyclic Carbene-Catalyzed Cross-Benzoin Reactions Using N-Boc-α-amino Aldehydes.

N-Boc-α-amino aldehydes are shown to be excellent partners in cross-benzoin reactions with aliphatic or heteroaromatic aldehydes. The chemoselectivity of the reaction and the facial selectivity on the amino aldehyde allow cross-benzoin products to be obtained in good yields and good diastereomeric ratios. The developed method is utilized as the key step in a concise total synthesis of d-arabino-phytosphingosine.