Asymmetric 1,3-Dipolar Cycloaddition Reactions

Organic chemists have always been fascinated by the cyclopropane subunit.1 The smallest cycloalkane is found as a basic structural element in a wide range of naturally occurring compounds.2 Moreover, many cyclopropane-containing unnatural products have been prepared to test the bonding features of this class of highly strained cycloalkanes3 and to study enzyme mechanism or inhibition.4 Cyclopropanes have also been used as versatile synthetic intermediates in the synthesis of more functionalized cycloalkanes5,6 and acyclic compounds.7 In recent years, most of the synthetic efforts have focused on the enantioselective synthesis of cyclopropanes.8 This has remained a challenge ever since it was found that the members of the pyrethroid class of compounds were effective insecticides.9 New and more efficient methods for the preparation of these entities in enantiomerically pure form are still evolving, and this review will focus mainly on the new methods that have appeared in the literature since 1989. It will elaborate on only three types of stereoselective cyclopropanation reactions from olefins: the halomethylmetal-mediated cyclopropanation reactions (eq 1), the transition metal-catalyzed decomposition of diazo compounds (eq 2), and the nucleophilic addition-ring closure sequence (eqs 3 and 4). These three processes will be examined in the context of diastereoand enantiocontrol. In the last section of the review, other methods commonly used to make chiral, nonracemic cyclopropanes will be briefly outlined.

Stereoselective Cyclopropanation Reactions

Donor-acceptor-substituted cyclopropane derivatives and their application in organic synthesis.

The electronic properties and relatively small size of fluorine endow it with considerable versatility as a bioisostere and it has found application as a substitute for lone pairs of electrons, the hydrogen atom, and the methyl group while also acting as a functional mimetic of the carbonyl, carbinol, and nitrile moieties. In this context, fluorine substitution can influence the potency, conformation, metabolism, membrane permeability, and P-gp recognition of a molecule and temper inhibition of the hERG channel by basic amines. However, as a consequence of the unique properties of fluorine, it features prominently in the design of higher order structural metaphors that are more esoteric in their conception and which reflect a more sophisticated molecular construction that broadens biological mimesis. In this Perspective, applications of fluorine in the construction of bioisosteric elements designed to enhance the in vitro and in vivo properties of a molecule are summarized.

Fluorine and Fluorinated Motifs in the Design and Application of Bioisosteres for Drug Design.

Standards and Guidelines for the Interpretation and Reporting of Sequence Variants in Cancer: A Joint Consensus Recommendation of the Association for Molecular Pathology, American Society of Clinical Oncology, and College of American Pathologists

The p53 tumor suppressor is a potent transcription factor that plays a key role in the regulation of cellular responses to stress It is controlled by its negative regulator MDM2, which binds directly to p53 and inhibits its transcriptional activity MDM2 also targets p53 for degradation by the proteasome Many tumors produce high levels of MDM2, thereby impairing p53 function Restoration of p53 activity by inhibiting the p53-MDM2 interaction may represent a novel approach to cancer treatment RG7112 (2g) is the first clinical small-molecule MDM2 inhibitor designed to occupy the p53-binding pocket of MDM2 In cancer cells expressing wild-type p53, RG7112 stabilizes p53 and activates the p53 pathway, leading to cell cycle arrest, apoptosis, and inhibition or regression of human tumor xenografts

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Discovery of RG7112: A Small-Molecule MDM2 Inhibitor in Clinical Development.

MDM2 negatively regulates p53 stability and many human tumors overproduce MDM2 as a mechanism to restrict p53 function. Thus, inhibitors of p53-MDM2 binding that can reactivate p53 in cancer cells may offer an effective approach for cancer therapy. RG7112 is a potent and selective member of the nutlin family of MDM2 antagonists currently in phase I clinical studies. RG7112 binds MDM2 with high affinity ( K D ∼ 11 nmol/L), blocking its interactions with p53 in vitro. A crystal structure of the RG7112–MDM2 complex revealed that the small molecule binds in the p53 pocket of MDM2, mimicking the interactions of critical p53 amino acid residues. Treatment of cancer cells expressing wild-type p53 with RG7112 activated the p53 pathway, leading to cell-cycle arrest and apoptosis. RG7112 showed potent antitumor activity against a panel of solid tumor cell lines. However, its apoptotic activity varied widely with the best response observed in osteosarcoma cells with MDM2 gene amplification. Interestingly, inhibition of caspase activity did not change the kinetics of p53-induced cell death. Oral administration of RG7112 to human xenograft-bearing mice at nontoxic concentrations caused dose-dependent changes in proliferation/apoptosis biomarkers as well as tumor inhibition and regression. Notably, RG7112 was highly synergistic with androgen deprivation in LNCaP xenograft tumors. Our findings offer a preclinical proof-of-concept that RG7112 is effective in treatment of solid tumors expressing wild-type p53. Cancer Res; 73(8); 2587–97. ©2013 AACR .

https://cancerres.aacrjournals.org/content/canres/73/8/2587.full.pdf

MDM2 Small-Molecule Antagonist RG7112 Activates p53 Signaling and Regresses Human Tumors in Preclinical Cancer Models

The total synthesis of the HMG-CoA synthase inhibitor 1233A (1), starting from either (R)-pulegone (6) or diketo ester 12, is described. The key transformations included the diastereoselective [2,3] rearrangements of allylic ethers 9 and 19 to alcohols 10 and 11b, respectively, and the diastereoselective hydroboration of 11b to form 19. A Pd-mediated coupling of iodo olefin 31a with tert-butyl crotonate under newly devised conditions provides an efficient preparation of the diene portion of 1233A

Peter Michael Wovkulich

Papers

Discovery of RG7112: A Small-Molecule MDM2 Inhibitor in Clinical Development.

MDM2 Small-Molecule Antagonist RG7112 Activates p53 Signaling and Regresses Human Tumors in Preclinical Cancer Models

Total synthesis of 1233A

Direct α-iodination of cycloalkenones

Total synthesis of acosamine and daunosamine utilizing a diastereoselective intramolecular [3+2] cycloaddition