Comprehensive study of okaspirodiol: characterization, total synthesis, and biosynthesis of a new metabolite from Streptomyces

The new spiro[4.5]acetal okaspirodiol (4) was isolated from Streptomyces sp. G? TS 19 as a secondary metabolite in yields up to 380 mg/L. The structure of this cryptic ketotetrol was elucidated by different methods including X-ray analysis, and its equilibration under mildly acidic conditions furnishing three additional isomers was thoroughly studied. Although metabolite 4 is not the thermodynamically favored isomer, a high-yielding total synthesis was accomplished comprising a stereoselective spiroacetalization under equilibrium conditions. This approach benefits from the important influence of an intramolecular hydrogen bond on the stabilization of the spiro[4.5]acetal moiety. The biosynthesis of 4 was investigated by feeding experiments with 13C-labeled precursors proving its origin from a new type of the rare mixed acetate-glycerol biosynthetic pathway. All results are discussed on the basis of the structural diversity of spiroacetals in nature and their chemical properties.     

Kinetics of thermal rearrangements in the Delta2-Thujene system: a full quadrisection of a perturbed bicyclo[3.1.0]hex-2-ene

Further insight into the behavior of suppositional diradicals in a caldera is sought in the thermal rearrangements among the four "Delta2-thujenes", two 1-isopropyl-4-methylbicyclo[3.1.0]hex-2-enes [(-)-cis-1 and (+)-trans-2] and two isomers, exo- and endo-3-isopropyl-6-methylbicyclo[3.1.0]hex-2-ene [(+)-exo-3 and (-)-endo-4]. Optically pure trans-3-isopropyl-5-vinylcyclopentene (5) is the final, strongly thermochemically favored product, the result of an intramolecular homodienyl shift of a methyl hydrogen atom in (-)-endo-4. The set of twelve specific rate constants, four sets of three each, that define the interrelations among the four isomers has been extracted from data acquired starting from each isomer. An attractive mechanistic hypothesis involving an intermediate diradical of iso conformation, common, for example, to both (-)-cis-1 and (+)-exo-3 (as educts), that proceeds to an anticonformer common to both (+)-trans-2 and (-)-endo-4 does not lead to a satisfactory rationalization of the product distribution. Addition of a second mechanistic conceptual scheme, that of a diradical-in-transit behaving as if there were a measure of continuous bonding (for example, (+)-trans-2 proceeding directly to (-)-cis-1), improves agreement with experiment. Over a 30 degrees C range of temperature, there is no credible change in product distribution.     

3D-2D-3D photonic crystal heterostructures fabricated by direct laser writing

Using direct laser writing, we fabricate photoresist templates for 3D-2D-3D photonic crystal heterostructures for what we believe to be the first time. The optical properties of these structures are directly compared with the theoretical ideal, revealing good agreement and hence good sample quality. This provides an experimental starting point for the microfabrication and testing of broadband, 3D air-waveguide microcircuitry in photonic bandgap materials.     

Detection of Blainville’s beaked whales with towed arrays

The detection performance of a towed hydrophone array for deep-diving species is quantified by comparing detections of echolocation clicks from foraging groups of Blainville’s beaked whales (Mesoplodon densirostris) from the TNO Delphinus array to detections from bottom-mounted hydrophones at the Atlantic Undersea Test and Evaluation Center (AUTEC) in the Bahamas. A beaked whale group detection probability of 40% is obtained at close ranges (R < 2000 m) with the Delphinus towed array, and a maximum detection range of 5000 m is measured. The detection function can be explained by models, when taking into account the range in rms source levels (200-220 dB re 1 μPa² m²), and the high system noise levels during the experiment. The model results suggest that detection ranges up to about 7 km are possible under favourable conditions, and demonstrate the effectiveness of using towed arrays to monitor deep-diving species, such as beaked whales.     

Occurrence and consequences of differences in the cation/anion ratios during classical resolution: D‐/L‐serine benzyl ester 2,3‐toluyl‐D‐tartrate

Differences in physical‐chemical properties of diaste‐reomeric salts allow the separation into the respective salts and subsequently into enantiomers by crystallization. Within this study unusual deviations in the cation‐/anion‐ratio of a diastereomeric salt pair were observed and characterized. While the n‐salt (L‐serine benzyl ester 2,3‐toluyl‐D‐tartrate) crystallizes in a ratio of two cations and one anion, the p‐salt (D‐serine benzyl ester 2,3‐toluyl‐D‐tartrate) consists of only one cation and one anion. Consequently the classical definition of a diastereomeric salt pair does not apply. In this contribution all differences in relevant thermodynamic properties of the unusual resulting diastereomeric salt pair are presented and discussed.     

Cascade Carbopalladation Reaction between Alkynes and gem-Dibromoolefins: Facile Access to Monoannelated Pentalenes

A carbopalladation cascade reaction of easily accessible gem-dibromoolefins and alkynes furnishes monobenzo- and mononaphthopentalenes. The new chromophores accessed by this short route exhibit small HOMO-LUMO gaps and redox amphoteric behavior with tunable redox potentials.