β-Decamethoxysapphyrin and Its N-Benzyl Analogue

Total synthesis of (+)-spiroindimicin A and congeners unveils their antiparasitic activity

The spiroindimicins are a unique class of chlorinated indole alkaloids characterized by three heteroaromatic rings structured around a congested spirocyclic stereocenter. Here, we report the first total synthesis of (+)-spiroindimicin A, which bears a challenging C-3′/C-5′′-linked spiroindolenine. We detail our initial efforts to effect a biomimetic oxidative spirocyclization from its proposed natural precursor, lynamicin D, and describe how these studies shaped our final abiotic 9-step solution to this complex alkaloid built around a key Pd-catalyzed asymmetric spirocyclization. Scalable access to spiroindimicins A, H, and their congeners has enabled discovery of their activity against several parasites relevant to human health, providing potential starting points for new therapeutics for the neglected tropical diseases leishmaniasis and African sleeping sickness.

Spiroindimicins A and H have been synthesized for the first time via a key palladium-catalyzed spirocyclization. Access to these alkaloids and several congeners has allowed the discovery of their antiparasitic properties.

Dibenzoylbenzodipyrroles: Key Precursors for the Synthesis of Fused meso-Aryl Sapphyrins

A simple strategy has been developed for the synthesis of α,α'-dibenzoylbenzodipyrroles, which are key synthons for the synthesis of fused porphyrinoids. α,α'-Dibenzoylbenzodipyrroles were characterized by high-resolution mass spectrometry (HRMS), NMR, and X-ray crystallography. To show the use of α,α'-dibenzoylbenzodipyrrole, we synthesized five different fused meso-aryl sapphyrins under acid-catalyzed reaction conditions. α,α'-Dibenzoylbenzodipyrrole was reduced to diol and condensed with five different tripyrranes such as aza, oxa, thia, selena, and telluratripyrranes under mild acid-catalyzed conditions to afford fused meso-aryl sapphyrins in 15-18% yields. One-dimensional (1D) and two-dimensional (2D) NMR studies revealed that in fused sapphyrins, the furan ring in oxabenzosapphyrin and the pyrrole ring in benzosapphyrin, which are present opposite to the benzodipyrrole moiety, attained ring inversion (inverted sapphyrins), whereas the selenophene ring in selenabenzosapphyrin and the tellurophene ring in tellurabenzosapphyrin did not show ring inversion (normal sapphyrins). However, thiabenzosapphyrin exhibits both normal and inverted conformations in different ratios. All fused sapphyrins showed typical aromatic absorption features; however, the absorption features of normal fused sapphyrins are different from the inverted fused sapphyrins. Redox studies indicate that normal fused sapphyrins are difficult to oxidize but easier to reduce compared to inverted fused sapphyrins. Density functional theory (DFT) studies support the experimental observations.

Flexible Porphyrinoids

This review underscores the conformational flexibility of porphyrinoids, a unique class of functional molecules, starting from the smallest triphyrins(1.1.1) via [18]porphyrins(1.1.1.1) and concluding with a variety of expanded porphyrinoids and heteroporphyrinoids, including the enormous [96]tetracosaphyrin(1.0.1.0.1.0.1.0.1.0.1.0.1.0.1.0.1.0.1.0.1.0.1.0). The specific flexibility of porphyrinoids has been documented as instrumental in the designing or redesigning of macrocyclic frames, particularly in the search for adjustable platforms for coordination or organometallic chemistry, anion binding, or mechanistic switches in molecular devices. A structural prearrangement to coordinate one or more metal ions has been outlined. The coverage of the topic focuses on representative examples of geometry or conformational rearrangements for each selected class of the numerous porphyrinoids accordingly categorized by the number of built-in carbo- or heterocycles.