Stereoselective synthesis and absolute configuration of the C33-C42 fragment of symbiodinolide

Cross-metathesis of methyl ester which was prepared from symbiodinolide with ethylene was performed to give the C33-C42 degraded fragment. This fragment was estimated to be (36S,40S)-diol by the modified Mosher method. Stereoselective synthesis of the (36S,40S)-diol and its diastereomer (36R,40S)-diol was achieved from l-aspartic acid. Synthetic bis-(S)- and (R)-MTPA esters which were derivatized from the (36S,40S)-diol exhibited spectroscopic data identical with those of bis-(S)- and (R)-MTPA esters derived from the degraded product. Thus, the absolute stereochemistry of the C33-C42 fragment was elucidated to be (36S,40S).     

Enantioselective, chemoenzymatic synthesis, and absolute configuration of the antioxidant (−)-gloeosporiol

The natural antioxidant (−)-gloeosporiol, isolated as a peracetylated derivative from a culture of the fungus Colletotrichum gloeosporioides, has been enantioselectively prepared from 3,4-dihydroxybenzaldehyde by means of a chemoenzymatic synthesis. The key intermediate was obtained by resolution with a lipase from Pseudomonas cepacia. Its stereochemistry, initially assigned as R, according to the Kazlaukas empirical rule for secondary alcohols, was independently confirmed by NMR and chirooptic methods. This, in turn, allowed the assignment of compound (−)-1 as (−)-(2S,3R,4R)-2-(3′,4′dihydroxyphenyl)tetrahydrofuran-3,4-diol.     

Structural revision and absolute configuration of lateritin

‘Lateritin’ (1), a morpholine-2,5-dione (depsipeptide), was reinvestigated for its structure and absolute configuration. On the basis of thorough 1D and 2D NMR and mass spectrometrical analyses, the structure of 1 was revised to be identical with beauvericin (8) and confirmed that beauvericin (8) is the trimeric lactone of ‘lateritin’ (1). The absolute configuration was determined by acidic hydrolysis, followed by application of Marfey’s method, menthyl ester derivatization, and GC–MS analysis. In addition, the specific optical rotation values of the hydrolysis products were compared with those of available standards.     

Synthesis and absolute configuration of (−)-chettaphanin I and (−)-chettaphanin II

An efficient synthesis of chettaphanin I and II has been achieved from ent-halimic acid. The absolute configuration of the natural products was established by nOe experiment and by X-ray analysis of chettaphanin II.     

Confirmation of the absolute configuration of (−)-aurantioclavine

We confirm our previous assignment of the absolute configuration of (−)-aurantioclavine as 7R by crystallographically characterizing an advanced 3-bromoindole intermediate reported in our previous synthesis. This analysis also provides additional support for our model of enantioinduction in the palladium(II)-catalyzed oxidative kinetic resolution of secondary alcohols.     

Study on the absolute configuration of (−)-palau’amine

The absolute stereochemistry of the immunosuppressive pyrrole-imidazole alkaloid (−)-palau’amine from the marine sponge Stylotella aurantium is analyzed by CD spectroscopy. With the help of a series of model compounds it is shown that the CD spectrum of (−)-palau’amine can be explained based on the assumption that the pyrrolopyrazinone partial structure is planar in 2,2,2-trifluoroethanol (TFE). Surprisingly, the natural product (−)-dibromophakellin shows the opposite Cotton effect, despite exhibiting the same absolute configuration.     

Synthesis and structural determination of the C33-C42 fragment of symbiodinolide

Symbiodinolide (1) is a polyol macrolide with a molecular weight of 2859 mu. As one of the degradation reactions, cross-metathesis of 2, which is a methyl ester of 1, with ethylene was performed to give the C33-C42 degraded fragment 4. The absolute configuration of 4 was estimated to be (36S,40S) by Mosher method. Stereoselective synthesis of 4 was achieved in 14 steps from l-aspartic acid. Synthetic bis-(S)- and (R)-MTPA esters exhibited the spectroscopic data identical with those of bis-(S)- and (R)-MTPA esters derived from the degraded fragment 4. Thus, the absolute stereochemistry of 4 was elucidated to be (36S,40S).     

Vanchrobactin: absolute configuration and total synthesis

The stereochemistry of vanchrobactin, a siderophore produced by the bacterial fish pathogenVibrio anguillarum serotype O2, was elucidated by chiral capillary electrophoresis analysis and total synthesis as N-[N′-(2,3-dihydroxybenzoyl)-d-arginyl]-l-serine.     

Structure and absolute configuration of penicilliumine,a new alkaloid from Penicillium commune 366606

Penicilliumine (1), a new structure was isolated from the fermentation Penicillium commune 366606, a marine-derived fungus isolated from the sea water collected at Qingdao, China. HPLC chiral separation of 1 afforded two enantiomers (−)-penicilliumine and (+)-penicilliumine, respectively. The structure of 1 was established by comprehensive spectroscopic data, and single-crystal X-ray diffraction. The absolute configuration of enantiomers was determined by quantum mechanical computation of electronic circular dichroism (ECD).     

Asymmetric synthesis of a diastereomer of the structure proposed for amphidinolide A and the determination of its absolute configuration

An asymmetric synthesis of a diastereomer (2) of the structure (1) proposed for amphidinolide A, a cytotoxic macrolide from the cultured dinoflagellate Amphidinium sp., has been accomplished. The absolute configuration of amphidinolide A was established as 3 from comparison of NMR data, HPLC analysis, and [α]_D values of amphidinolide A, and comparison with the synthetic diastereomers 2 and 3, the latter of which was synthesized previously by Trost's group.     

Enantioselective synthesis and absolute configuration of the sex pheromone of Hedypathes betulinus (Coleoptera: Cerambycidae)

The male-produced sex pheromone of Hedypathes betulinus was identified as a mixture of (E)-6,10-dimethyl-5,9-undecadien-2-one (geranylacetone) (1) and its respective alcohol (2) and acetate (3). Kinetic resolution of alcohol (2) promoted by CAL-B in organic media provided both, (R)-(−)-(E)-6,10-dimethyl-5,9-undecadien-2-yl acetate (3) and (S)-(+)-(E)-6,10-dimethyl-5,9-undecadien-2-ol (2) in high enantiomeric purity. Comparative GC analysis using a chiral column revealed the natural constituents as being (R)-(3) and a mixture of (R)- and (S)-(2) in a ratio of 82.3% and 17.6%, respectively.     

Synthesis of a novel sphingosine kinase inhibitor (−)-F-12509A and determination of its absolute configuration

The synthesis of a novel sphingosine kinase inhibitor, (−)-F-12509A ((−)-1), was achieved in a highly efficient manner that included nine longest linear steps and 45% overall yield from (−)-bicyclic β-ketoester (−)-2, and its absolute configuration was determined to be (5S,9S,10S).     

Synthesis of brasilibactin A and confirmation of absolute configuration of β-hydroxy acid fragment

A synthesis of brasilibactin A, a cytotoxic siderophore from the actinomycete of Nocardia brasiliensis, and three unnatural diastereomers of the natural product is described. Four possible diastereomers of the β-hydroxy acid fragment were prepared via asymmetric aldol reactions and used to synthesize brasilibactin A and its diastereomers. Careful analysis of ¹H NMR data confirmed that brasilibactin A possesses the 17S,18R absolute stereochemistry.     

Diverse prieurianin-type limonoid derivatives from the fruits of Aphanamixis grandifolia and their absolute configuration determination

Twenty-five new highly oxygenated prieurianin-type limonoids, zaphaprinins A–Y (1–25), were isolated from the fruits of Aphanamixis grandifolia. Their structures were elucidated by extensive spectroscopic analyses. Absolute configurations for the key structures like 1 were assigned by a comprehensive method, such as comparing the calculated electronic circular dichroism (ECD) with the experimental one, single-crystal X-ray and Mosher ester method were also involved for other compounds' study. The solid data from X-ray diffraction allowed revision of the stereochemistry of the C₁–C₁₄ tetrahydropyran ring-type limonoid. The insecticidal activities of all the limonoids were evaluated.     

Structure and absolute configuration of 3-alkylpiperidine alkaloids from an Indonesian sponge of the genus Halichondria

Chemical analysis of an Indonesian sponge sample has provided three new 3-alkylpiperidine alkaloids, tetradehydrohaliclonacyclamine A, its mono-N-oxide derivative, and a 2-epi isomer. The absolute structure of tetradehydrohaliclonacyclamine A has been established by X-ray crystallography from anomalous dispersion effects using Cu radiation, which determined that the absolute configuration is 2S, 3S, 7S, 9S while an HPLC study revealed that the alkaloid is enantiomerically pure.     

Total syntheses of (+)- and (−)-1,3,4,5-tetragalloylapiitol and revision of absolute configuration of naturally occurring (−)-1,3,4,5-tetragalloylapiitol

The total syntheses of (+)- and (−)-1,3,4,5-tetragalloylapiitol were achieved in seven steps from d- and l-ribose, respectively. By comparing the optical rotations of both enantiomers with those of the natural product, the absolute configuration at C-3 in the naturally occurring 1,3,4,5-tetragalloylapiitol has been revised to R. The absolute configurations at C-3 in the synthetic (+)- and (−)-1,3,4,5-tetragalloylapiitol were further confirmed by the circular dichroism exciton chirality method.     

Synthesis and assignment of the absolute stereochemistry of (+)-hemifistularin 3

The first total synthesis of the marine natural product (+)-hemifistularin 3 in enantiomerically pure form was accomplished by using the amide forming reaction of (+)-spiroisoxazoline ester with the (+)-octopamine derivative. The stereodivergent strategy employed in this effort enabled the assignment of the absolute configurations at the three stereogenic centers in (+)-hemifistularin 3.     

Structure determination and absolute configuration of cannabichromanone derivatives from high potency Cannabis sativa

Three new cannabichromanone derivatives were isolated from high potency cannabis, along with the known cannabichromanone. Full spectroscopic data, including the use of electronic circular dichroism and Mosher ester analysis to determine the absolute configuration of these compounds, are reported. All isolates were tested for antimicrobial, antimalarial, antileishmanial, and anti-oxidant activities.     

Synthesis of cordiaquinone J and K via B-alkyl Suzuki-Miyaura coupling as a key step and determination of the absolute configuration of natural products

A versatile methodology for the synthesis of various terpenoids via B-alkyl Suzuki-Miyaura coupling as a key step is established. Synthesis of cordiaquinone J and K, new antifungal and larvicidal meroterpenoids, was achieved by using this methodology. The absolute configurations of cordiaquinone J and K were confirmed by the synthesis.