Synthesis and Antibacterial Activity of Four Stereoisomers of the Spider-Pathogenic Fungus Metabolite Torrubiellone D

Total synthesis and stereochemistry establishment of tumescenamide A

Tumescenamide A (1), isolated from Streptomyces tumescens YM23-20, consists of a cyclic depsipeptide and a side-chain 2,4-dimethylheptanoate (Dmh).

Dual Agents: Fungal Macrocidins and Synthetic Analogues with Herbicidal and Antibiofilm Activities

Eight analogues of the bioherbicides macrocidin A (1) and Z (2) with structural variance in the size of the macrocycle, its para- or meta-cyclophane character, and its functional groups were synthesized on two modular routes and tested for herbicidal, antibiotic, and antibiofilm activities. Apart from the lead compounds 1 and 2, the structurally simplified dihydromacrocidin Z (3) and normacrocidin Z (4) showed high herbicidal activity in either thistles, dandelions or in both. The derivatives 2, 3, and dibromide 9 also inhibited the growth of Staphylococcus aureus biofilms by ca 70% when applied at subtoxic concentrations as low as ca 20 µM, which are unlikely to induce bacterial resistance. They also led to the dispersion of preformed biofilms of S. aureus, exceeding a similar effect by microporenic acid A, a known biofilm inhibitor. Compounds 3 and 9 showed no noticeable cytotoxicity against human cancer and endothelial cells at concentrations below 50 µM, making them conceivable candidates for application as anti-biofilm agents in a medicinal context.

Recent applications of the Wittig reaction in alkaloid synthesis

The Wittig reaction is the chemical reaction of an aldehyde or ketone with a triphenyl phosphonium ylide (the Wittig reagent) to afford an alkene and triphenylphosphine oxide. Noteworthy, this reaction results in the synthesis of alkenes in a selective and predictable fashion. Thus, it became as one of the keystone of synthetic organic chemistry, especially in the total synthesis of natural products, where the selectivity of a reaction is paramount of importance. A literature survey disclosed the existence of vast numbers of related reports and comprehensive reviews on the applications of this important name reaction in the total synthesis of natural products. However, the aim of this chapter is to underscore, the applications of the Wittig reaction in the total synthesis of one the most important and prevalent classes of natural products, the alkaloids, especially those showing important and diverse biological activities.

Discovery of natural products with metal-binding properties as promising antibacterial agents

INTRODUCTION

More than 50% of the clinically established antibiotics are either genuine natural products or derivatives thereof, featuring a mode of action decisively depending on their metal affinity and suitability as metal complex ligands. As their structural diversity and harvest from renewable sources is well-nigh inexhaustible, any future quest for affordable new antibiotics will have to concentrate on natural drugs with obvious metal ligating properties. Areas covered: The authors provide an overview of the promising developments in the field of antibiotic natural products with metal-binding properties with a specific focus on metal binders such as polyphenols, quinones, 3-acyltetramic and -tetronic acids. Works published by the authors are discussed in this manuscript as well as articles derived from PubMed and Scifinder. Expert opinion: Natural products with metal-binding properties possess a great potential for the development of drugs against various bacteria. There are many derivatives with great potential against multidrug-resistant bacteria as well. Synthetic approaches to structurally complex and/or rare natural products have added significantly to the cracking of synthetic problems. Thus, this field of scientific research appears attractive both to chemists and to clinicians.

Chemical and Biological Aspects of Nutritional Immunity-Perspectives for New Anti-Infectives that Target Iron Uptake Systems

Upon bacterial infection, one of the defense mechanisms of the host is the withdrawal of essential metal ions, in particular iron, which leads to "nutritional immunity". However, bacteria have evolved strategies to overcome iron starvation, for example, by stealing iron from the host or other bacteria through specific iron chelators with high binding affinity. Fortunately, these complex interactions between the host and pathogen that lead to metal homeostasis provide several opportunities for interception and, thus, allow the development of novel antibacterial compounds. This Review focuses on iron, discusses recent highlights, and gives some future perspectives which are relevant in the fight against antibiotic resistance.

Multifunctional odorless isocyano(triphenylphosphoranylidene)-acetates: synthesis and direct one-pot four-component Ugi/Wittig cyclization to multisubstituted oxazoles

A new one-step four-component synthesis of multisubstituted oxazoles has been developed.

Total Synthesis and Biological Evaluation of Hybrubin A

Here, we report the first total synthesis of hybrubin A, a bipyrrole tetramic acid alkaloid representing a new carbon framework derived from convergent (truncated red cluster and exogenous hbn cluster) biosynthetic pathways. A highly convergent synthesis was developed, employing 4-methoxy-1,5-dihydro-2H-pyrrol-2-one (13) as a single starting material to provide hybrubin A in three steps from 13 and 20.8% overall yield. As no biological activity was prescribed to hybrubin A except for a lack of cytotoxicity, we further profiled this unique alkaloid across panels of discrete molecular targets. Interestingly, hybrubin A was found to be a ligand for a variety of GPCRs with a propensity for potent binding across therapeutically relevant adenosine receptors (A₁, A_2a, and A₃) as well as a potent activity at a kinase, FLT3. This pattern of biological activity is distinct from other related prodigiosin natural and unnatural products and is even more intriguing in the absence of cytotoxicity.