α-Carbonyl Rh-Carbenoid Initiated Cascade Assembly of Diazobarbiturates with Alkylidene Pyrazolones for Synthesis of Spirofuropyrimidines

Catalyzed by Rh2(esp)2 (10 mol%) and (±)-BINAP (20 mol%) in DCE at 80 °C, the cascade assembly between diazobarbiturates and alkylidene pyrazolones proceeded readily and produced spiro-furopyrimidines in 38-96% chemical yields. The chemical structure of the prepared spirofuro-pyrimidines was firmly confirmed by X-ray diffraction analysis.

Facile and diastereoselective arylation of the privileged 1,4-dihydroisoquinolin-3(2H)-one scaffold

A practically convenient and streamlined protocol for the trans-diastereoselective introduction of an aryl substituent at position 4 of the 1,4-dihydroisoquinol-3-one (1,4-DHIQ) scaffold is presented. The protocol involves direct Regitz diazo transfer onto readily available 3(2H)-isoquinolones followed by TfOH-promoted hydroarylation by an arene molecule. Screening of the novel 1,2,4-trisubstituted 1,4-DHIQs against cancer cell lines confirmed high cytotoxicity of selected analogs, which validates this new chemotype for further investigations as anticancer cytotoxic agents.

Unexpected Ring Contraction of Homophthalic Anhydrides under Diazo Transfer Conditions

An attempted Regitz diazo transfer onto homophthalic anhydride led to the discovery of an unexpected ring contraction, which gave N-sulfonyl phthalide-3-carboxamide derivatives. The reaction is thought to proceed via a [3 + 2] cycloaddition of the substrate's enol form and the azide followed by a two-step fragmentation of the intermediate 1,2,3-triazoline with a loss of the nitrogen molecule.

Natural-Like Spirocyclic Δα,β -Butenolides Obtained from Diazo Homophthalimides

α-Diazo homophotalimides were reacted with various propiolic acids on Rh₂ (esp)₂ catalysis. The resulting propiolate esters were transformed into novel, heterocyclic Δ^α,β -spirobutenolides in good to excellent product yields. The approach represents a fundamentally novel entry into natural-like Δ^α,β -spirobutenolides present in many biologically active natural products as well as fully synthetic compounds endowed with diverse biological activities. The Δ^α,β -spirobutenolides thus obtained were shown to inhibit thioredoxin reductase, a selenocysteine enzyme target for cancer. Moreover, for the best compound in the series (TrxR IC₅₀ 1.49±0.08 μM), by using MALDI-TOF mass-spectrometry it was shown that it selectively binds selenocysteine in the presence of a 10-fold excess of cysteine. This validates the new compound as a promising lead for anticancer therapy development.

4-Benzylideneisoquinoline-1,3(2H,4H)-diones as tyrosyl DNA phosphodiesterase 2 (TDP2) inhibitors

Tyrosyl-DNA phosphodiesterase 2 (TDP2) repairs topoisomerase II (Top2) mediated DNA damages, including double-strand breaks (DSBs) that underpin the anticancer mechanism of clinical TOP2 poisons such as etoposide (ETP). Inhibition of TDP2 could sensitize cancer cells toward TOP2 poisons by increasing Top2 cleavage complex. We have previously identified isoquinoline-1,3-dione as a selective inhibitor type of TDP2. However, the reported structure-activity relationship (SAR) was limited to simple substitutions on the isoquinoline-1,3-dione core. Herein, we report the extended SAR consisting of the synthesis and testing of a total of 50 analogs featuring N-2 and C-4 modifications. Major SAR observations include the loss of potency upon N-2 substitution, the lack of inhibition with C-4 enamine analogs (subtype 11), or any other C-4 modifications (subtypes 13-15) except for the benzylidene substitution (subtype 12), where eight analogs showed low micromolar potency. The best analog, 12q, inhibited TDP2 with an IC50 of 4.8 μM. Molecular modeling was performed to help understand the observed SAR trends. Overall, these SAR observations which could significantly benefit future work on the design of improved TDP2 inhibitors.

Preparation and in situ use of unstable N-alkyl α-diazo-γ-butyrolactams in RhII-catalyzed X-H insertion reactions

N-Alkyl α-diazo-γ-butyrolactams, previously found to be unstable and to undergo unproductive dimerization to bishydrazones, were successfully converted immediately to various X–H insertion products with alcohols, aromatic amines and thiols via an in situ Rh^II-catalyzed reaction. With aliphatic amines or unreactive, sterically hindered anilines, the reactions tended to yield enamine adducts.

Superelectrophiles in Synthesis: Preparation of Aromatic Imides

Aromatic carboxylic acids are found to undergo reactions with isocyanates, wherein triflic acid promotes the formation of aromatic imide products in fair to good yields. It is proposed that the carboxylic acid group directs the isocyanate electrophile to the ortho-position. This is thought to occur by the formation of a temporary carbamic acid anhydride group, which cleaves upon ortho-functionalization. A series of imide products are synthesized, and the synthesis of a potential selective inhibitor of tyrosyl DNA phosphodiesterase II is performed.