Indole alkaloids are a diverse class of natural products known for their wide range of biological activities and complex chemical structures. Rarely observed in this class are indolic nitrones, such as avrainvillamide and waikialoid, which possess potent bioactivities. Herein the oxa gene cluster from the marine-derived fungus Penicillium oxalicum F30 is described along with the characterization of OxaD, a flavin-dependent oxidase that generates roquefortine L, a nitrone-bearing intermediate in the biosynthesis of oxaline. Nitrone functionality in roquefortine L was confirmed by spectroscopic methods and 1,3-dipolar cycloaddition with methyl acrylate. OxaD is a versatile biocatalyst that converts an array of semisynthetic roquefortine C derivatives bearing indoline systems to their respective nitrones. This work describes the first implementation of a nitrone synthase as a biocatalyst and establishes a novel platform for late-stage diversification of a range of complex natural products.

The oxidation of roquefortine C to the nitrone roquefortine L was investigated using a number of different electrophilic oxidizing reagents. mCPBA and Oxone were shown to be the most effective in achieving this transformation, while unfavorable steric interactions precluded oxidation by bulky reagents such as Davis oxaziridine. Finally, each of the oxidants was shown to promote aromatic hydroxylation following the synthesis of the nitrone functionality.

Natural products bearing a triazaspirocyclic motif have received significant attention in recent years. These compounds, which feature three nitrogen atoms attached to one quaternary carbon forming a spirocyclic scaffold, exhibit a wide range of biological activity and have promising applications in materials as well as in drug discovery. In this review article, we will discuss triazaspirocycles in Nature, their biological activity, and applications. Methods for the synthesis of triazaspirocycles as well as the reactivity of triazaspirocyclic scaffolds will be reviewed.

Laboratory courses in universities have a responsibility to introduce current research practices and trends in scientific research to adequately prepare students for work in the field. One such research practice gaining popularity in recent years is that of green chemistry. Since the 1960s, increasing concern over the release of toxic chemicals into the environment has led to a push for more environmentally responsible chemistry. A growing faction of chemists has begun to adopt methods to eliminate chemical waste and support green chemistry. Fermentation is an ideal technique to demonstrate environmentally sustainable chemistry in an undergraduate laboratory class. Fermentation of complex natural products, as opposed to traditional organic synthesis, is beneficial as it supports a number of principles of green chemistry; it is conducted at ambient temperature and pressure, uses inexpensive and innocuous materials, makes use of renewable resources, and does not require a fume hood. Skills implemented during fermentation can be easily taught to upper-level Chemistry and Biochemistry undergraduate students, who typically have limited exposure to complex natural products in their coursework. Such a course would be interdisciplinary in nature, incorporating fungal biology and metabolism as well as organic chemistry. Students would learn a variety of skills, including growth media selection and preparation, inoculation of fungal cultures, extraction of natural products, and purification and characterization of metabolites. Experiments of this nature would allow for discussions of several areas of research: green chemistry, natural products and their application to medicine, identification of functional groups in complex molecules by spectroscopy, and introduction to biochemistry and metabolism. Roquefortine C, a prenylated indole alkaloid readily produced by a variety of species of Penicillia, is an excellent candidate for demonstrating fermentation in a laboratory classroom setting, owing to its ease of purification from other metabolites and its unique structural features.