The l-Alanosine Gene Cluster Encodes a Pathway for Diazeniumdiolate Biosynthesis

N-Nitroso-containing natural products are bioactive metabolites with antibacterial and anticancer properties. In particular, compounds containing the diazeniumdiolate (N-nitrosohydroxylamine) group display a wide range of bioactivities ranging from cytotoxicity to metal chelation. Despite the importance of this structural motif, knowledge of its biosynthesis is limited. Herein we describe the discovery of a biosynthetic gene cluster in Streptomyces alanosinicus ATCC 15710 responsible for producing the diazeniumdiolate natural product l-alanosine. Gene disruption and stable isotope feeding experiments identified essential biosynthetic genes and revealed the source of the N-nitroso group. Additional biochemical characterization of the biosynthetic enzymes revealed that the non-proteinogenic amino acid l-2,3-diaminopropionic acid (l-Dap) is synthesized and loaded onto a free-standing peptidyl carrier protein (PCP) domain in l-alanosine biosynthesis, which we propose may be a mechanism of handling unstable intermediates generated en route to the diazeniumdiolate. These discoveries will facilitate efforts to determine the biochemistry of diazeniumdiolate formation.

Synthetic studies toward citrinadin A: construction of the pentacyclic core

This manuscript describes the preparation of an advanced intermediate toward the total synthesis of citrinadin A, featuring a [3+2] cycloaddition employing in situ generation of the dipole.

Collaborative Total Synthesis: Routes to (±)-Hippolachnin A Enabled by Quadricyclane Cycloaddition and Late-Stage C-H Oxidation

Described herein are synthetic efforts toward the synthesis of hippolachnin A. Two independently devised routes from the Brown and Wood groups allowed for the synthesis of hippolachnin A from the unusual starting material, quadricyclane, by harnessing the power of late-stage C-H oxidation. Collaborative union of the best features of the two routes allowed for preparation of the molecule with improved efficiency.

Synthetic studies toward the citrinadins: enantioselective preparation of an advanced spirooxindole intermediate

This manuscript describes the enantioselective preparation of a spirooxindole that is suited for advancedment to either Citrinadin A or B.

Computer tracking as a behavioral GC detector: Nematode responses to vapor of host roots

A computer tracking system previously developed for studying the behavioral responses of nematodes to volatile stimuli was modified so that the effluent of a gas chromatograph passed over the nematodes while their behavior was analyzed. Since the behavior of several hundred nematodes can be analyzed simultaneously, this technique has the potential to provide a sensitive assay for behaviorally active fractions from the GC. This potential was tested with infective juveniles of the root-knot nematodeMeloidogyne incognita and vapor from the roots of host tomato plants. Direct injection of 1 ml of vapor led to reproducible responses at times corresponding to nitrogen plus oxygen elution and to carbon dioxide elution. Experiments with pure gases demonstrated responses to oxygen and to carbon dioxide. Attempts were made to find less volatile and less active components by pulling large volumes of vapor through a trap of Tenax GC and subsequently eluting them onto the GC. This approach did not lead to the detection of other activities. We conclude that, other than carbon dioxide, there are no volatile stimuli released from host roots in effective quantities.

An enantioselective total synthesis and stereochemical revision of (+)-citrinadin B

This manuscript describes an enantioselective synthesis of the naturally occurring alkaloid citrinadin B. The synthetic effort revealed an anomaly in the original structural assignment that has led to the proposal of a stereochemical revision. This revision is consistent with the structures previously reported for a closely related family of alkaloids, PF1270A-C. The synthesis is convergent and employs a stereoselective intermolecular nitrone cyloaddition reaction as a key step.

Effect of dexamethasone on experimental brain edema in cats

The authors studied the effects of dexamethasone, 0.3 mg/kg/hr administered intravenously beginning 1 hour before injury, in adult cats with brain edema secondary to cold-induced cortical lesions. Edema was quantitatively measured in cortex, gyral white matter, and central (deep) white matter at 3, 24, 48, and 72 hours, with and without dexamethasone, by determining specific gravity (density) of samples in a continuous gradient column. Cold-induced lesions resulted in edema, which was greatest in the white matter of the injured hemisphere but also present in the contralateral hemisphere. Except for a slight but significant increase in density (decreased edema) of cortex at 24 hours, dexamethasone therapy resulted in no reduction of cold-induced edema, and in some cases increased the edema.

Diamonds in an Upper Mantle Peridotite Nodule from Kimberlite in Southern Wyoming

Diamonds in a serpentinized garnet peridotite nodule from a diatreme in southern Wyoming are the first known occurrence in an upper mantle peridotite xenolith from a kimberlite intrusion in North America as well as the second authenticated occurrence of diamonds from kimberlite pipes in North America. The nodule is believed to have come from a section of depleted (partially melted) lherzolite at a depth of 130 to 180 kilometers.