Cyclopiazonic Acid and Okaramine Analogues, Including Chlorinated Compounds, from Chrysosporium undulatum YT-1

A Survey of Recently Discovered Naturally Occurring Organohalogen Compounds

The discovery of naturally occurring organohalogen compounds has increased astronomically in the 55 years since they were first discovered─from fewer than 50 in 1968 to a combined 7,958 described examples in three comprehensive reviews. The present survey, which covers the period 2021-2023, brings the number of known natural organohalogens to approximately 8,400. The organization is according to species origin, and coverage includes marine and terrestrial plants, fungi, bacteria, marine sponges, corals, cyanobacteria, tunicates, and other marine organisms.

Genomic and Comparative Transcriptomic Analyses Reveal Key Genes Associated with the Biosynthesis Regulation of Okaramine B in Penicillium daleae NBP-49626

Restricted production of fungal secondary metabolites hinders the ability to conduct comprehensive research and development of novel biopesticides. Okaramine B from Penicillium demonstrates remarkable insecticidal efficacy; however, its biosynthetic yield is low, and its regulatory mechanism remains unknown. The present study found that the yield difference was influenced by fermentation modes in okaramine-producing strains and performed genomic and comparative transcriptome analysis of P. daleae strain NBP-49626, which exhibits significant features. The NBP-49626 genome is 37.4 Mb, and it encodes 10,131 protein-encoding genes. Up to 5097 differentially expressed genes (DEGs) were identified during the submerged and semi-solid fermentation processes. The oka gene cluster, lacking regulatory and transport genes, displayed distinct transcriptional patterns in response to the fermentation modes and yield of Okaramine B. Although transcription trends of most known global regulatory genes are inconsistent with those of oka, this study identified five potential regulatory genes, including two novel Zn(II)2Cys6 transcription factors, Reg2 and Reg19. A significant correlation was also observed between tryptophan metabolism and Okaramine B yields. In addition, several transporter genes were identified as DEGs. These results were confirmed using real-time quantitative PCR. This study provides comprehensive information regarding the regulatory mechanism of Okaramine B biosynthesis in Penicillium and is critical to the further yield improvement for the development of insecticides.

Origin of the 6/5/6/5 Tetracyclic Cyclopiazonic Acids

The natural product α-cyclopiazonic acid (α-CPA) is a very potent Ca2+-ATPase inhibitor. The CPA family of compounds comprise over 80 chemical entities with at least five distinct skeletons. While α-CPA features a canonical 6/5/6/5/5 skeleton, the 6/5/6/5 skeleton is the most prevalent among the CPA family. However, the origin of the unique tetracyclic skeleton remains unknown. The 6/5/6/5-type CPAs may derive from a precursor of acetoacetyl-l-tryptophan (AATrp) generated from a hypothetic thioesterase-like pathway. Alternatively, cleavage of the tetramic acid ring would also result in the formation of the 6/5/6/5 scaffold. Aspergillus oryzae HMP-F28 is a marine sponge-associated filamentous fungus known to produce CPAs that act as primary neurotoxins. To elucidate the origin of this subfamily of CPAs, we performed homologous recombination and genetic engineering experiments on strain HMP-F28. Our results are supportive of the ring cleavage pathway through which the tetracyclic 6/5/6/5-type CPAs are generated from 6/5/6/5/5-type pentacyclic CPAs.

Organocatalyzed Enantioselective [2 + 2] Cycloaddition of C,N-Cyclic Ketimines and Allenoates

We report a novel enantioselective and regioselective [2 + 2] cycloaddition of allenoate and C,N-cyclic ketimine catalyzed by a quinidine derivative. The methodology enables the synthesis of fused tricyclic azetidines with a quaternary stereogenic center exhibiting high enantioselectivities. The broad range of substrates demonstrates the generality of the protocol, and the resulting functional products can be easily converted to a variety of valuable synthons. To elucidate the plausible reaction mechanism and how the catalyst affects absolute stereocontrol over the products, we conducted the corresponding density functional theory (DFT) calculations.

Pegriseofamines A-E: Five cyclopiazonic acid related indole alkaloids from the fungus Penicillium griseofulvum

Five new cyclopiazonic acid related indole alkaloids, pegriseofamines A-E (1-5), were isolated from the fungus Penicillium griseofulvum. Their structures and absolute configurations were determined by NMR, HRESIMS, quantum-chemical calculation, and X-ray diffraction experiments. Among them, pegriseofamine A (1) possesses an undescribed 6/5/6/7 tetracyclic ring system generated by the fusion of an azepine and an indole unit via a cyclohexane, and the postulated biosynthetic origin of 1 was discussed. Compound 4 could relieve liver injury and prevent hepatocyte apoptosis in ConA-induced autoimmune liver disease.