Total Synthesis of Isoprekinamycin: Structural Evidence for Enhanced Diazonium Ion Character and Growth Inhibitory Activity toward Cancer Cells

Cationic gold-catalyzed intramolecular cyclization of substituted 1,5-diynes to access indenone derivatives

An efficient intramolecular cyclization reaction was developed to achive indenone derivatives. The substituted 1,5-diyenes were converted to the cooresponding indenones via gold-catalyzed organic transformation and moderate to excellent yields of the title molecules were obatined via formation of two C=O and one C-C bonds under mild reaction condtions in one-pot.

Recursive Anion-Triggered Tandem Reactions of ortho-Bis-ynones: Tunable Synthesis of 1-Indenones and Cyclopenta[a]inden-8(2H)-ones

Recursive anion-mediated activation of o-bis-ynones sets off a Michael addition-aldol reaction-dehydrative rearrangement cascade, leading to the one-pot synthesis of 1-indenones via orthogonal interplay between the two ortho-ynone moieties. Repeating the recursive anion engagement with the 1-indenones unfolded access to a functionally embellished cyclopenta[a]inden-8(2H)-one core and its spiroannulated analogues either directly or stepwise through tandem 1,6-Michael-type addition-6π electrocyclization and an in situ oxidation sequence.

Lewis Acid Mediated Domino Intramolecular Cyclization: Synthesis of Dihydrobenzo[a]fluorenes

An efficient and facile method for the regioselective synthesis of novel dihydrobenzo[a]fluorenes from readily accessible alkynols is presented. The current strategy triggers the formation of a dual C-C bond intramolecularly via Lewis acid catalysis under mild reaction conditions. Notably, secondary as well as tertiary alcohols bearing an alkyne moiety have been smoothly transformed into the corresponding products. As a result, novel tetracyclic dihydrobenzo[a]fluorenes have been accomplished using this approach.

Ninhydrins inhibit carbonic anhydrases directly binding to the metal ion

Ninhydrins show extensive application in organic chemistry and agriculture whereas they have been poorly investigated as bioactive molecules for medicinal chemistry purposes. A series of ninhydrin derivatives was here investigated for the inhibition of human carbonic anhydrases (CAs, EC 4.2.1.1), based on earlier evidence that gem diols are able to coordinate the metal ion from the CA active site. Ninhydrins demonstrated a micromolar inhibitory action against CA I and IX (K_Is in the range 0.57-68.2 μM) and up to a nanomolar efficacy against CA II and VII (K_Is in the range 0.025-78.2 μM), validated isoforms as targets in several CNS-related diseases. CA IV was instead weakly or poorly inhibited. A computational protocol based on docking, MM-GBSA and metadynamics calculations was used to elucidate the putative binding mode of this type of inhibitors to CA II and CA VII. The findings of this study testify that such pharmacologically underestimated ligands may represent interesting lead compounds for the development of CA inhibitors possessing an innovative mechanism of action, i.e., mono- or bis-coordination to the zinc ion through the diol moiety.

Fukuyama Cross-Coupling Approach to Isoprekinamycin: Discovery of the Highly Active and Bench-Stable Palladium Precatalyst POxAP

An efficient and user-friendly palladium(II) precatalyst, POxAP (post-oxidative-addition precatalyst), was identified for use in Fukuyama cross-coupling reactions. Suitable for storage under air, the POxAP precatalyst allowed reaction between thioesters and organozinc reagents with turnover numbers of ∼90000. A series of 23 ketones were obtained with yields ranging from 53 to 99%. As proof of efficacy, an alternative approach was developed for the synthesis of a key precursor of the natural product isoprekinamycin.

Iodine-mediated synthesis of benzo[a]fluorenones from yne-enones

The chalcones derived from o-alkynylacetophenones and aromatic aldehydes (yne-enones) when heated under reflux with iodine in acetic acid gave a range of benzo[a]fluorenone derivatives in moderate to good yields. The transformation involves the formation of a vinyl indenone intermediate through regioselective alkyne hydration and intramolecular aldol condensation followed by electrocyclic ring closure and aromatization.

An iodine mediated synthesis of benzo[a]fluorenone derivatives from the chalcones derived from o-alkynylacetophenones and aromatic aldehydes is described.

A general strategy for diverse syntheses of anhydrolandomycinone, tetrangulol, and landomycinone

A protecting group promoted-CH arylation strategy for the total synthesis of landomycinone and related core structures.

Stereoselective synthesis of sulfonated 1-indenones via radical-triggered multi-component cyclization of β-alkynyl propenones

New radical-triggered multi-component cyclizations of β-alkynyl propenones have been developed, leading to 50 examples of sulfonated 1-indenones with generally good yields and high levels of stereoselectivity.

A gold-catalyzed cycloisomerization/aerobic oxidation cascade strategy for 2-aryl indenones from 1,5-enynes

The syntheses of 2-aryl indenones via gold(i)-catalyzed cyclization/aerobic oxidation was reported. The mechanism was probed by heavy atom labelling and control experiments. A formal total synthesis of isoprekinamycin was achieved.

Silver-mediated radical 5-exo-dig cyclization of 2-alkynylbenzonitriles: synthesis of phosphinylated 1-indenones

A new silver-mediated 5-exo-dig cyclization of 2-alkynylbenzonitriles with disubstituted phosphine oxide and H₂O has been developed.

Synthesis of 2,3-disubstituted indenones by cobalt-catalyzed [3+2] annulation of o-methoxycarbonylphenylboronic acid with alkynes

Treatment of alkynes with o-methoxycarbonylphenylboronic acid in the presence of a cobalt catalyst resulted in the corresponding 2,3-disubstituted indenones.

Converting potent indeno[1,2-b]indole inhibitors of protein kinase CK2 into selective inhibitors of the breast cancer resistance protein ABCG2

A series of indeno[1,2-b]indole-9,10-dione derivatives were synthesized as human casein kinase II (CK2) inhibitors. The most potent inhibitors contained a N(5)-isopropyl substituent on the C-ring. The same series of compounds was found to also inhibit the breast cancer resistance protein ABCG2 but with totally different structure-activity relationships: a N(5)-phenethyl substituent was critical, and additional hydrophobic substituents at position 7 or 8 of the D-ring or a methoxy at phenethyl position ortho or meta also contributed to inhibition. The best ABCG2 inhibitors, such as 4c, 4h, 4i, 4j, and 4k, behaved as very weak inhibitors of CK2, whereas the most potent CK2 inhibitors, such as 4a, 4p, and 4e, displayed limited interaction with ABCG2. It was therefore possible to convert, through suitable substitutions of the indeno[1,2-b]indole-9,10-dione scaffold, potent CK2 inhibitors into selective ABCG2 inhibitors and vice versa. In addition, some of the best ABCG2 inhibitors, which displayed a very low cytotoxicity, thus giving a high therapeutic ratio, and appeared not to be transported, constitute promising candidates for further investigations.

Prekinamycin and an isosteric-isoelectronic analogue exhibit comparable cytotoxicity towards K562 human leukemia cells

The diazo functionality of the kinamycins may not be an absolute requirement for bioactivity.

MeOTf-induced carboannulation of arylnitriles and aromatic alkynes: a new metal-free strategy to construct indenones

MeOTf-induced carboannulation of arylnitriles and aromatic alkynes for synthesis of indenones and their derivatives under metal-free conditions has been described.

Diels-Alder reactions using 4,7-dioxygenated indanones as dienophiles for regioselective construction of oxygenated 2,3-dihydrobenz[f]indenone skeleton

Regioselective construction of 4,8,9-trioxygenated 2,3-dihydrobenz[f]indenones, key intermediates for the synthesis of kinamycin antibiotics, was achieved via Diels-Alder reactions (DAR) using 4,7-dioxygenated indanone-type compounds as dienophiles. Reaction of indanetrione with 1-methoxybutadiene gave a 1 : 1 mixture of undesired 4,5,9-trioxygenated 2,3-dihydrobenz[f]indenone and [4.4.3]propellane. The addition of Lewis acid did not affect the product ratio, whereas the use of the 6-bromoindanetrione exclusively afforded the latter propellane. On the other hand, DAR of benzyne derived from bromoindan and furan gave 5,8-epoxy-2,3-dihydrobenz[f]indene, which was subjected to acid-induced ring opening to give 2,3-dihydrobenz[f]indenone with undesired 4,5,9-trioxy functions.