Synthesis of Benzannulated Medium-ring Lactams via a Tandem Oxidative Dearomatization-Ring Expansion Reaction.

Medium-ring natural products exhibit diverse biological activities but such scaffolds are underrepresented in probe and drug discovery efforts due to the limitations of classical macrocyclization reactions. We report herein a tandem oxidative dearomatization-ring-expanding rearomatization (ODRE) reaction that generates benzannulated medium-ring lactams directly from simple bicyclic substrates. The reaction accommodates diverse aryl substrates (haloarenes, aryl ethers, aryl amides, heterocycles) and strategic incorporation of a bridgehead alcohol generates a versatile ketone moiety in the products amenable to downstream modifications. Cheminformatic analysis indicates that these medium rings access regions of chemical space that overlap with related natural products and are distinct from synthetic drugs, setting the stage for their use in discovery screening against novel biological targets.

Principal component analysis as a tool for library design: a case study investigating natural products, brand-name drugs, natural product-like libraries, and drug-like libraries.

Principal component analysis (PCA) is a useful tool in the design and planning of chemical libraries. PCA can be used to reveal differences in structural and physicochemical parameters between various classes of compounds by displaying them in a convenient graphical format. Herein, we demonstrate the use of PCA to gain insight into structural features that differentiate natural products, synthetic drugs, natural product-like libraries, and drug-like libraries, and show how the results can be used to guide library design.

Biomimetic diversity-oriented synthesis of benzannulated medium rings via ring expansion.

Nature has exploited medium-sized 8- to 11-membered rings in a variety of natural products to address diverse and challenging biological targets. However, owing to the limitations of conventional cyclization-based approaches to medium-ring synthesis, these structures remain severely underrepresented in current probe and drug discovery efforts. To address this problem, we have established an alternative, biomimetic ring expansion approach to the diversity-oriented synthesis of medium-ring libraries. Oxidative dearomatization of bicyclic phenols affords polycyclic cyclohexadienones that undergo efficient ring expansion to form benzannulated medium-ring scaffolds found in natural products. The ring expansion reaction can be induced using three complementary reagents that avoid competing dienone-phenol rearrangements and is driven by rearomatization of a phenol ring adjacent to the scissile bond. Cheminformatic analysis of the resulting first-generation library confirms that these molecules occupy chemical space overlapping with medium-ring natural products and distinct from that of synthetic drugs and drug-like libraries.

A diastereoselective formal synthesis of berkelic acid.

A formal synthesis of berkelic acid is reported. The strategy employs the combination of a chiral exocyclic enol ether and an achiral isochromanone to afford the chroman spiroketal core via a base-triggered generation and cycloaddition of an o-quinone methide intermediate. Other key steps include equilibration of the spiroketal, intramolecular benzylic oxidation, and lactone addition/hemiketal reduction; all occur with good diastereoselectivity.

Dearomatization applications of I(III) reagents and some unusual reactivity amongst resorcinol derived cyclohexadienones.

The oxidative dearomatization of resorcinol derivatives, which are outfitted with a lactic acid derived chiral tether, and mitigated by hypervalent iodine derivatives of PhIO, affords stable chiral cyclohexadienones as useful building blocks for the construction of many highly functionalized chiral six and seven-membered ring systems. Herein, we report a multitude of remarkable and unexpected diastereoselective transformations stemming from these cyclohexadienone adducts.

Enantioselective total synthesis of all of the known chiral cleroindicins (C-F): clarification among optical rotations and assignments.

Enantioselective syntheses of all of the named chiral members of the cleroindicin family (C-F) are reported. This effort demonstrates the synthetic utility of a 2,4-dihydroxybenzaldehyde as a starting material for natural product synthesis through the use sequential o-quinone methide chemistry and diastereoselective dearomatization. Natural cleroindicin F was shown to be nearly racemic, and an optically pure synthetic sample of cleroindicin F was found to racemize under slightly basic conditions. All other natural chiral cleroindicins are shown to be partially racemic.

Synthesis of 2,2-Disubstituted Pentalenes and Indenes by a Useful Modification to Nakamura's DMCP [3+2]-Cycloaddition Protocol.

A two-pot tactic is presented to reach the oxidized 2,2-dimethyl-substituted pentalene and indene ring systems.