RESUMEN
Enantioselective construction of small molecules displaying a configurationally stable helical shape built on a fused-tetracyclic core is a daunting synthetic challenge even more pronounced when five-membered rings are incorporated in the structure. The resulting higher configurational lability strongly hampers their access, and therefore the development of new efficient methodologies is timely and highly desirable. In this context, we describe a padlocking approach via the enantioselective organocatalytic domino furannulation of appropriately designed achiral fused-tricyclic precursors resulting in the synthesis of configurationally locked helically chiral tetracyclic scaffolds featuring one or two five-membered rings with the simultaneous control of central and helical chiralities.
RESUMEN
[This corrects the article DOI: 10.1021/acsomega.2c05415.].
RESUMEN
Sponges are prolific producers of specialized metabolites with unique structural scaffolds. Their chemical diversity has always inspired natural product chemists working in drug discovery. As part of their metabolic filter-feeding activities, sponges are known to release molecules, possibly including their specialized metabolites. These released "Exo-Metabolites" (EMs) may be considered as new chemical reservoirs that could be collected from the water column while preserving marine biodiversity. The present work aims to determine the proportion and diversity of specialized EMs released by the sponge Aplysina cavernicola (Vacelet 1959). This Mediterranean sponge produces bromo-spiroisoxazoline alkaloids that are widely distributed in the Aplysinidae family. Aquarium experiments were designed to facilitate a continuous concentration of dissolved and diluted metabolites from the seawater around the sponges. Mass Spectrometry (MS)-based metabolomics combined with a dereplication pipeline were performed to investigate the proportion and identity of brominated alkaloids released as EMs. Chemometric analysis revealed that brominated features represented 12% of the total sponge's EM features. Consequently, a total of 13 bromotyrosine alkaloids were reproducibly detected as EMs. The most abundant ones were aerothionin, purealidin L, aerophobin 1, and a new structural congener, herein named aplysine 1. Their structural identity was confirmed by NMR analyses following their isolation. MS-based quantification indicated that these major brominated EMs represented up to 1.0 ± 0.3% w/w of the concentrated seawater extract. This analytical workflow and collected results will serve as a stepping stone to characterize the composition of A. cavernicola's EMs and those released by other sponges through in situ experiments, leading to further evaluate the biological properties of such EMs.
RESUMEN
Porphyrin cage-compounds are used as biomimetic models and substrate-selective catalysts in supramolecular chemistry. In this work we present the resolution of planar-chiral porphyrin cages and the determination of their absolute configuration by vibrational circular dichroism in combination with density functional theory calculations. The chiral porphyrin-cages form complexes with achiral and chiral viologen-guests and upon binding one of the axial enantiomorphs of the guest is bound selectively, as is indicated by induced-electronic-dichroism-spectra in combination with calculations. This host-guest binding also leads to unusual enhanced vibrational circular dichroism, which is the result of a combination of phenomena, such as rigidification of the host and guest structures, charge transfer, and coupling of specific vibration modes of the host and guest. The results offer insights in how the porphyrin cage-compounds may be used to construct a future molecular Turing machine that can write chiral information onto polymer chains.
RESUMEN
An expedient synthesis of a new family of configurationally stable dioxa[6]helicenes was established using a sequential helicoselective organocatalyzed heteroannulation/eliminative aromatization via enantioenriched fused 2-nitro dihydrofurans featuring both central and helical chiralities. Starting from simple achiral precursors, a broad range of these previously unknown chiral heterocyclic scaffolds were obtained with good efficiency, and their aromatization proceeded with very high enantiopurity retention in most cases.
