Chemometric Comparison of Thin-Layer Chromatography,Gradient High-Performance Liquid Chromatography,and Computational Methods for Lipophilicity Assessment of Model Compounds

JPC – Journal of Planar Chromatography – Modern TLC - Thin-layer chromatography (TLC) on two adsorbents (RP18 and CN) and with six modifiers (acetonitrile, acetone, dioxane, propan...     

Coralloidolide F,the First Example of a 2,6-Cyclized Cembranolide: Isolation from the Mediterranean Alcyonacean Coral Alcyonium coralloides

The Mediterranean alcyonacean Alcyonium ( = Parerythropodium) coralloides (Pallas, 1766) is shown here to contain coralloidolide F ( = (+)-(3a-R*, 7R*, 8R*, 9R*, 12R*, 12aS*)-8,9-epoxy-1,3a,6,7,8,9,10,11,12,12a-decahydro-3a-hydroxy-12-isopropenyl-2,5-dimethyl-1-oxocyclopfintacycloundecene-9,7-carbolactone; (+)- 2 ), the first example of a 2,6-cyclized cembranolide. Structural assignments are mainly based on ID and 2D NMR and MS data.     

Isolation of the Cembranoid Preverecynarmin Alongside Some Briaranes,the Verecynarmins,from Both the Nudibranch Mollusc Armina maculata and the Octocoral Veretillum cynomorium of the East Pyrenean Mediterranean Sea

It is shown that the nudibranch mollusc Armina maculata and its prey, the pennatulacean octocoral Veretillum cynomorium, of east Pyrenean waters contain a novel cembranoid, preverecynarmin ((+)- 8 ), besides the known cembranoid cembrene C ( 9 ) and three further briarane diterpenoids (verecynarmin E ((?)- 5 ), F ((?)- 6 ), and G ((?)- 7 )). A biogenetic scheme is proposed.     

Calenzanane sesquiterpenes from the red seaweed Laurencia microcladia from the Bay of Calenzana, Elba Island: acid-catalyzed stereospecific conversion of calenzanol into indene- and guaiazulene-type sesquiterpenes

It is shown here that calenzanane sesquiterpenes (1 and 6) can be isolated from organic extracts from the red seaweed Laurencia microcladia Kützing from the Bay of Calenzana, Elba Island, provided contact with acidic media is minimized. Such contact induces rearrangements of 1 in dry solvents to indene-type 5 and the blue-colored guaiazulenium-type ion 17, via spectrometrically (NMR) characterized indene-type transient intermediates 10, 14, and 12. Addition of NEt(3) to the reaction mixture at appropriate stages allowed the isolation of 12 (and 8 on workup on SiO(2)), and guaiazulene (18). Prolonged contact with silica gel led to complete degradation of 1, giving calenzanane-type epimeric enones 20 a/20 b as well as indene-type epimeric carbinols 22 a/22 b and fulvene 7. The latter was also formed during silica-gel flash chromatography of the algal extracts. A unifying mechanistic view of these branching and cascade transformations may have both heuristic value, suggesting possible artefact origin of azulenoids, and synthetic applications.     

Novel 10-Hydroxydocosapolyenoic Acids from Deep-Water Scleractinian Corals

The new 10-hydroxydocosapolyenoic acids (10R,7Z,11E,13E,16Z,19Z)-10-hydroxydocosa-7,11,13,16,19-pentaenoic acid ( 1a ) and (10R*,4Z,7Z,11E,13Z,16Z,19Z)-10-hydroxydocosa-4,7,11,13,16,19-hexaenoic acid ( 2a ) were isolated as methyl esters 1b and 2b , respectively, following CH₂N₂ treatment of the EtOH extract of the scleractinian coral Madrepora oculata from deep-water of the southern Indian Ocean. From the same species from the Norwegian Sea, 1b and the methyl ester 3b of the new (10R,7Z,11E,13Z,16Z)-10-hydroxydocosa-7,11,13,16-tetraenoic acid ( 3a ) were analogously isolated, while from the untreated extract, the free acid 3a itself could be isolated. The absolute configuration of 1a and 3a was established by the chiral exciton coupling of the C(10) benzoate esters 1c and 3c . Other known 10-hydroxydocosapolyenoic acids and 8-hydroxyeicosapolyenoic acid were also isolated from M. oculata from both locations. These results imply the intervention of a rare lipooxygenase with high ω13 specificity. In an examination of several other deep-water scleractinians, hydroxypolyenoic acids were found only in Lophelia pertusa from the northeastern Atlantic Ocean.     

Leucascandrolide B,a New 16-Membered,Extensively Methyl-Branched Polyoxygenated Macrolide from the Calcareous Sponge Leucascandra caveolata from Northeastern Waters of New Caledonia

We report a novel, extensively methyl-branched and polyoxygenated 16-membered macrolide, leucascandrolide B (=(1R*,5S*,7R*,9S*,13R*,14R*,15R*,11Z)-5-[(E)-1,4-dimethylhept-5-enyl]-1,7,9-trihydroxy-11,14-dimethyl-3-oxo-4,17-dioxabicyclo[11.3.1]heptadec-11-en-15-yl] carbamate; 2 ), isolated from the calcareous sponge Leucascandra caveolata Borojevic and Klautau from the northeastern coast of New Caledonia. The NMR structural assignments were corroborated by semisynthetic derivatives of 2 , the functional groups and atom connectivity by derivatives 4 – 6 (obtained by acetylation, oxidation, and elimination-solvation, resp.), and the relative configurations by derivative 7 (obtained by carbonation). The preferred conformation of 2 , centered on a chair-like tetrahydro-2H-pyran ring formed by intramolecular acetalization, was derived from molecular mechanics and semiempirical calculations which were in agreement with all NMR data. A dilactone `dimeric' structure 3 , indistinguishable from 2 on the basis of all above data, was ruled out by tandem MS-MS experiments.     

A New‐Skeleton Diterpenoid,New Prenylbisabolanes,and Their Putative Biogenetic Precursor,from the Red Seaweed Laurencia microcladia from Il Rogiolo: Assigning the Absolute Configuration when Two Chiral Halves are Connected By Single Bonds

We report here a new‐skeleton tricyclic diterpenoid, neorogioldiol ( 8 ), along with new prenylbisabolanes, rogioldiol D ( 6 ) and O¹¹,15‐cyclo‐14‐bromo‐14,15‐dihydrorogiol‐3,11‐diol ( 5 ), and their putative biogenetic precursor, (−)‐geranyllinalool ( 7 ), isolated from the red seaweed Laurencia microcladia, which has colonized a small tract of the Tuscany coast called Il Rogiolo. In a case study of the assignment of the absolute configuration for molecules composed of chiral halves that are connected by single bonds, the absolute configuration of neorogioldiol ( 8 ) was based on a) the assumption of the identity of the cyclohexane moiety with co‐occurring (2S,3R,6S)‐rogiolal ( 4 ) and b) NMR‐derived relative configurations for the bicyclic moiety, and c) the combination of these two pieces of information by molecular‐mechanics‐aided conformational analysis, in agreement with NOE data.