Isolation and absolute configuration determination of aliphatic sulfates as the Daphnia kairomones inducing morphological defense of a phytoplankton-part 2

4,8-Dimethylnonyl sulfate (1) and 3-methyl-4E-decenyl sulfate (2) were isolated from Daphnia pulex as the Daphnia kairomones that induced morphological defense of a freshwater phytoplankton Scenedesmus gutwinskii var. heterospina (NIES-802). The absolute configuration at C4 of 1 was determined by Ohrui's method applied to alcohol 3. The absolute stereochemistry at C3 of 2 was determined by (1)H-NMR analysis of the (R)-1NMA ester of alcohol 11.     

Isolation of new aliphatic sulfates and sulfamate as the Daphnia Kairomones inducing morphological change of a phytoplankton Scenedesmus gutwinskii

New aliphatic sulfates and sulfamates were isolated from Daphnia pulex as the Daphnia kairomones that induced morphological defense of a freshwater phytoplankton Scenedesmus gutwinskii var. heterospina (NIES-802). Their structures were determined by spectroscopic and synthetic studies.     

Aliphatic sulfates released from Daphnia induce morphological defense of phytoplankton: isolation and synthesis of kairomones

Six aliphatic sulfates, kairomones released from a crustacean Daphnia pulex induce morphological changes of phytoplankton Scenedesmus gutwinskii at ppb (10⁻⁹ g/mL) concentrations.     

Isolation and absolute configuration determination of alkaloids from Pandanus amaryllifolius

Seven new alkaloids belonging to three typical classes, isolated from an ethanolic extract of Pandanus amaryllifolius, were applied to establish the models in structural elucidation. The first type [pandanusines A and B (1 and 2)] was applied to alkaloids with a diazaspirocyclic ring system. The absolute stereochemistry of aminal carbon is determined by analysis of J-based configuration analysis and circular dichroism spectroscopy, which has never been revealed before. The second type [pandalizines C–E (3–5)], the stereochemistry of unusual indolizinone with chiral hydroxyl substitutions were determined by circular dichroism spectroscopy and vibrational circular dichroism experiments. The last type [norpandamarilactonines C and D (6 and 7)], a comparing model in determination of diastereomers of pyrrolidinyl α,β-unsaturated γ-lactone alkaloids was established. Our study provides solutions for a challenging subject in stereochemistry determination for three different types of Pandanus alkaloids.     

A chemical/computational approach to the determination of absolute configuration of flexible and transparent molecules: aliphatic diols as a case study

By reacting flexible and optically transparent in UV-vis molecules such as 1,2-, syn- and anti-1,3-diols, 1,3-sulfanylalcohols of known absolute configuration (AC) with fluorenone dimethyl acetal, the corresponding ketals are obtained. They are conformationally well-defined (only one conformer in most cases) compounds exhibiting medium-high optical rotation (OR) values, which are independent of the solvent, and electronic circular dichroism (ECD) spectra, which show several (up to five) Cotton effects in the 350-200 nm range due to valence shell pi-->pi* transitions. These features allow simulation of the chiroptical properties of these compounds at the TDDFT/B3LYP/6-31G* level of theory to obtain, using the known ACs of these compounds, a satisfactory reproduction of the OR values (sign and order of magnitude; quantitatively, the predicted values are twice the experimental ones), and a more than satisfactory reproduction of the ECD spectra (sign, intensity, and position of the lowest-energy four Cotton effects) for all the compounds studied. Therefore, this approach can be used to assign the AC of such flexible molecules, in particular, syn-1,3-diols, which are important substrates in organic synthesis and for which nonempirical methods of AC assignment have not been devised so far. Furthermore, since the fluorene chromophore leads to the presence of several Cotton effects from, say, 350 to 200 nm, their correct simulation of sign, intensity, and position is a guarantee of the correct assignment of AC: in this way, ECD spectroscopy gains the same advantages of VCD spectroscopy, that is, the need of reproducing many ECD bands and then a solid guarantee of a correct AC assignment.     

Helicity induction in a bichromophore: a sensitive and practical chiroptical method for absolute configuration determination of aliphatic alcohols

[reaction: see text] A practical method for the determination of the absolute configuration of aliphatic secondary alcohols, based on the circular dichroism of the readily available N-(1,8-naphthaloyl)-2-aminobenzoyl (NAB) derivative, is presented. The origin of the induced Cotton effects is traced by ab initio calculations to the dominant helicity of the NAB pi-electron system.     

Cyclic chiral silyl derivatives for the determination of the absolute configuration of aliphatic diols by gas chromatography

[reaction: see text] Chiral bidentate silyl reagents have been developed for the GC analysis of aliphatic 1,3- and 1,4-diols. These reagents react with the diols to cyclic siloxanes, which allow the determination of their enantiomeric composition even in complex mixtures. The absolute configuration of 4,6-nonadecanediol 7, occurring in the lipids of sunflower pollen, has been determined to be (4S,6R) by comparison with derivatized synthetic enantiomers.     

Application of the cd homoallylic benzoate method as a chiroptical tool for determination of absolute configuration

After the conformation I was clarified to 5α-,10α,-cis-solidagolactones by ¹H NMR measurement with Eu(dpm)₃ and chemical transformations, the CD homoallylic benzoate chirality method was applied to the homoallylic alcohol system of solidagolactone IV ($\text{1a}$) for a chiroptical determination of the absolute configuration. The result agreed with absolute configuration elucidated by x-ray analysis, indicating the usefulness of the cd method.     

Monosaccharides as internal probes for the determination of the absolute configuration of 2-butanol

D-Glucose, D-mannose and L-rhamnose were reacted with a racemic mixture of 2-butanol, and the resulting alpha-glycosides were analyzed by 1H NMR with COSY and NOESY experiments. Conformational analysis of alpha-glycosidic bonds performed with molecular modeling and appropriate heteronuclear long-range coupling measurements and combined with analysis of dipolar couplings observed in NOESY spectra allowed the assignment of absolute configuration in the aglycones of elucidated alpha-glycosides.     

Synthesis and determination of the absolute configuration of chiral tetracosanaphthalenes

Tetracosanaphthalenes with diethylaminocarbonylmethoxy side chains were constructed by bottom-up synthesis, and their absolute configurations were determined by an exciton chirality method.     

Total synthesis and determination of the absolute configuration of (+)-neoisoprelaurefucin

The first total synthesis of the seven-membered ring ether marine natural product (+)-neoisoprelaurefucin (1) has been achieved employing a regioselective internal alkylation of amide 3, a novel sequence for removal of the triethylsilyl group from the resulting triethylsilyloxepene 2, and a bromoetherification of alcohol 16 as key steps. In addition, the absolute stereochemistry of the natural product was assigned.     

Synthesis of the saccharomicin fucose-aglycon conjugate and determination of absolute configuration

[reaction: see text] Schmidt glycosylation of the appropriately protected 3,4-dihydroxycinnamate methyl ester with 2,3,4-triacetoxyfucopyranosyltrichloroacetimidate gives aryl glycoside in high yield and diastereoselectivity. 2-Sulfation of fucose, installation of taurine, and global deprotection of the remaining protecting groups affords the fucose-aglycon conjugate of saccharomicin. This synthesis which arises from L-fucose also establishes the absolute configuration of the reducing terminus of the saccharomicin oligosaccharide.     

Direct determination of the absolute configuration of a cyclic thiolsulfinate by VCD spectroscopy

Experimental and calculated vibrational circular dichroism (VCD) spectra of the enantiomers of the conformationally rigid thiolsulfinate, naphtho[1,8-cd]-1,2-dithiole 1-oxide 1, obtained by chromatographic resolution of the racemate, were in excellent agreement, showing a (+)-(S)-1/(−)-(R)-1 relationship.     

Synthesis and determination of the absolute configuration of the macrodiolide (+)-conglobatin

(+)-Conglobatin is synthesized from (-)-(2S,4R)-2.4-dimethyl glutaric acid half-ester in 15 steps (total yield 4.4%). The synthesis proves the sense of chirality of the natural (-)-conglobatin to be opposite to the one previously assigned.     

Stereoselective synthesis of kurzilactone and determination of its absolute configuration

Both (5S,7S)- and (5R,7S)-isomers of kurzilactone were synthesized from a ‘chiral epoxy-aldehyde synthon’ through the coupling of an acyl anion equivalent and the dianion of acetoacetate, followed by formation of the Kawa-type lactone by cyclization and elimination. Comparing the spectral data of the synthesized and naturally occurring kurzilactone, the C(5)- and C(7)-stereogenic centers of the natural kurzilactone was assigned a corrected anti-relationship with (5R,7S)-absolute configuration.     

Synthesis of chiral isoquinuclidines and determination of their absolute configuration

A route to 1,2-dihydropyridines N¹-substituted with chiral auxiliaries has been developed starting from commercially available chiral amines. Cycloaddition between these dihydropyridines and methyl acrylate gave, in moderate d.e., isoquinuclidines of good enantiomeric purity whose absolute configuration has been established.     

Isolation of an anthrabenzoxocinone 1.264-C from Streptomyces sp. FXJ1.264 and absolute configuration determination of the anthrabenzoxocinones

The anthrabenzoxocinones (ABXs) are hexacyclic aromatic compounds with various bioactivities. Some ABXs with two stereogenic carbon centers have been isolated from different actinomycetes. However, none of them have an absolute configuration assigned, which precludes further studies on the structure–activity relationship and biosynthetic mechanisms of the ABXs. An ABX compound 1.264-C was isolated from Streptomyces sp. FXJ1.264. The absolute configuration of 1.264-C was characterized by X-ray crystallographic, electronic, and experimental circular dichroism (CD) analyses. Based on the reported CD and specific rotation data, the absolute configurations of several other ABXs were also assigned.     

A new determination of the absolute configuration of the chiral amine

A new method for assignment of the absolute configuration of the asymmetric carbon atom attached to an amino or imino group using rac.-3-hexadecanoyl-4-methoxycarbonyl-1,3-thiazolidine-2-thione (rac.-HDMTT) ($\text{4}$) is described.