Identification and Heterologous Expression of the Albucidin Gene Cluster from the Marine Strain Subsp. NRRL B-24108.

Herbicides with new modes of action and safer toxicological and environmental profiles are needed to manage the evolution of weeds that are resistant to commercial herbicides. The unparalleled structural diversity of natural products makes these compounds a promising source for new herbicides. In 2009, a novel nucleoside phytotoxin, albucidin, with broad activity against grass and broadleaf weeds was isolated from a strain of subsp.

The Synthesis of Certain Phomentrioloxin A Analogues and Their Evaluation as Herbicidal Agents.

A series of 28 analogues of the phytotoxic geranylcyclohexentriol (-)-phomentrioloxin A (1) has been synthesized through cross-couplings of various enantiomerically pure haloconduritols or certain deoxygenated derivatives with either terminal alkynes or borylated alkenes. Some of these analogues display modest herbicidal activities, and physiological profiling studies suggest that analogue 4 inhibits photosystem II in isolated thylakoids in vitro.

Screening of Panamanian Plant Extracts for Pesticidal Properties and HPLC-Based Identification of Active Compounds.

A library of 600 taxonomically diverse Panamanian plant extracts was screened for fungicidal, insecticidal, and herbicidal activities. A total of 19 active extracts were submitted to HPLC-based activity profiling, and extracts of Bocconia frutescens, Miconia affinis, Myrcia splendens, Combretum aff. laxum, and Erythroxylum macrophyllum were selected for the isolation of compounds.

Cyclobutanes in catalysis.

The exploitation of ring strain as a driving force to facilitate chemical reactions is a well-appreciated principle in organic chemistry. The most prominent and most frequently used compound classes in this respect are oxiranes and cyclopropanes. For rather a long time, cyclobutanes lagged behind these three-membered-ring compounds in their development as reactive substrates, but during the past decade an increasing number of useful reactions of four-membered-ring substrates have emerged.

Enantioselective rhodium-catalyzed C-C bond activations.

The catalytic activation of carbon-carbon single bonds represents a major challenge in organometallic chemistry. Strained ring substrates occupy in this respect a privileged role as their inherent ring strain facilitates the desired metal insertion. Employing symmetrically substituted tert-cyclobutanols, an enantioselective rhodium(I)-catalyzed beta-carbon elimination creates alkyl-rhodium species bearing all-carbon quaternary stereogenic centers.

Rhodium-catalyzed C-C bond cleavage: construction of acyclic methyl substituted quaternary stereogenic centers.

A rhodium-catalyzed enantioselective insertion into the C-C bond of tert-cyclobutanols and subsequent proto-demetalation provides access to methyl substituted quaternary stereogenic centers in excellent yields and enantioselectivities. The reaction was used for a synthesis of (S)-4-ethyl-4-methyl-octane, the simplest saturated hydrocarbon with a quaternary stereogenic center.

Rhodium(I)-catalyzed enantioselective activation of cyclobutanols: formation of cyclohexane derivatives with quaternary stereogenic centers.

The activation of carbon-carbon sigma bonds is a complementary method to access uncommon and difficult-to-prepare organometallic species. Herein, we describe the activation of tert-cyclobutanols through an enantioselective insertion of a chiral rhodium(I) complex into the C-C sigma bond of the cyclobutane, forming a quaternary stereogenic center and an alkyl-rhodium functionality that initiates ring-closure reactions. This technology provides access to a variety of substituted cyclohexane derivatives with quaternary stereogenic centers.

Enantioselective metal-catalyzed activation of strained rings.

Activation of otherwise inert bonds has significant potential in the design of efficient and synthetically useful transformations. While general catalytic carbon-carbon single bond activations are still in their infancy, this emerging area examines recent developments in the activation of strained rings, focusing on enantioselective reactions.