ABSTRACT
Antimicrobial multidrug resistance (MDR) is a global challenge, not only for public health, but also for sustainable agriculture. Antibiotics used in humans should be ruled out for use in veterinary or agricultural settings. Applying antimicrobial peptide (AMP) molecules, produced by soil-born organisms for protecting (soil-born) plants, seems a preferable alternative. The natural role of peptide-antimicrobials, produced by the prokaryotic partner of entomopathogenic-nematode/bacterium (EPN/EPB) symbiotic associations, is to sustain monoxenic conditions for the EPB in the gut of the semi-anabiotic infective dauer juvenile (IJ) EPN. They keep pathobiome conditions balanced for the EPN/EPB complex in polyxenic (soil, vanquished insect cadaver) niches. Xenorhabdus szentirmaii DSM16338(T) (EMC), and X. budapestensis DSM16342(T) (EMA), are the respective natural symbionts of EPN species Steinernema rarum and S. bicornutum. We identified and characterized both of these 15 years ago. The functional annotation of the draft genome of EMC revealed 71 genes encoding non-ribosomal peptide synthases, and polyketide synthases. The large spatial Xenorhabdus AMP (fabclavine), was discovered in EMA, and its biosynthetic pathway in EMC. The AMPs produced by EMA and EMC are promising candidates for controlling MDR prokaryotic and eukaryotic pathogens (bacteria, oomycetes, fungi, protozoa). EMC releases large quantity of iodinin (1,6-dihydroxyphenazine 5,10-dioxide) in a water-soluble form into the media, where it condenses to form spectacular water-insoluble, macroscopic crystals. This review evaluates the scientific impact of international research on EMA and EMC.
ABSTRACT
The initial goal of this work was to verify the geometry of the product of a photochemical reaction, viz. the title compound, C(8)H(10)O(6)S, (II). Our crystallographic study firmly establishes the cis-anti-cis nature of the substituents on the cyclobutane ring. The geometry is also designated as exo, where exo signifies that the five-membered ring is on the opposite side of the central cyclobutane ring from the carboxylic acid substituents. The structure determination reveals two molecules, A and B, in the asymmetric unit that display substantially different conformations of the bicyclic core: the cyclobutane ring puckering angles are 22 and 3 degrees , and the sulfolane ring conformations are twist (S-exo) and envelope (S-endo). Intrigued by this variation, we then compared the conformations of other molecules in the Cambridge Structural Database that have sulfolane rings fused to cyclobutane rings. In this class of compound, there are five examples of saturated cyclobutane rings, with ring puckering angles ranging from 3 to 35 degrees . The sulfolane rings were more similar: four of the six molecules exhibit envelope conformations with S-endo, as in molecule B of (II). Despite the conformational differences, the hydrogen-bonding scheme for both molecules is similar: carboxyl -OH groups form hydrogen bonds with carboxyl and sulfone O atoms. Alternating A and B molecules joined by hydrogen bonds between sulfone O atoms and carboxyl -OH groups form parallel chains that extend in the ac plane. Other hydrogen bonds between the carboxyl groups link the chains along the b axis.
ABSTRACT
The reaction of 2-chloro-5-nitropyridine with two equivalents of base produces the title carbanion as an intermediate in a ring-opening/ring-closing reaction. The crystal structures of the tetra-n-butylammonium salts of the intermediates, C(16)H(36)N(+).C(5)H(3)N(2)O(3)(-), revealed that pseudo-cis and pseudo-trans isomers are possible. One crystal structure displayed a mixture of the two isomers with approximately 90% pseudo-cis geometry and confirms the structure predicted by the S(N)(ANRORC) mechanism. The pseudo-cis intermediate undergoes a slow isomerization over a period of months to the pseudo-trans isomer, which does not have the appropriate geometry for the subsequent ring-closing reaction. The structure of the pure pseudo-trans isomer is also reported. In both isomers, the negative charge is highly delocalized, but relatively small differences in C-C bond distances indicate a system of conjugated double bonds with the nitro group bearing the negative charge. The packing of the two unit cells is very similar and largely determined by the interactions between the planar carbanion and the bulky tetrahedral cation.
ABSTRACT
The reaction of 2-chloro-3-nitropyridine with two equivalents of hydroxide ion was studied by NMR and X-ray crystallography. On the basis of NMR coupling constants, the originally formed ring-opened intermediate is the pseudo-cis form, as predicted by the SN(ANRORC) mechanism. However, the first intermediate is unstable and isomerizes to a second intermediate, which was isolated. The pseudo-trans geometry of the second intermediate [3-pentenenitrile, 2-nitro-5-oxo, ion(-1), sodium] explains why additional base does not lead to the ring-closing reaction as observed with 2-chloro-5-nitropyridine.
ABSTRACT
The title five-membered heterocycle, C4H4Cl2OS, adopts an envelope conformation with the S atom at the tip of the flap. All three ring substituents, viz. the sulfoxide O atom and the two Cl atoms, are cis to each other. The two C atoms alpha to the sulfoxide group are also bonded to chlorine. The electron-withdrawing chlorine substituents give rise to weak C-H...O hydrogen bonds with the sulfoxide O atom of a symmetry-related molecule [H...O = 2.44 (2) and 2.61 (2) A, C...O = 3.143 (3) and 3.302 (2) A and C-H...O = 129.9 (19) and 135.1 (19) degrees ]. There is also a possible weak C-H...Cl interaction. Chains of molecules held together by these weak interactions run parallel to the a axis.
