New strategy for the total synthesis of macrosphelides a and B based on ring-closing metathesis

[reaction: see text] A new total synthesis of macrosphelides A and B using ring-closing metathesis (RCM) as a macrocyclization step is described. The substrate of the RCM could be synthesized from readily available chiral materials, methyl (S)-(+)-3-hydroxybutyrate and methyl (S)-(-)-lactate, with a high efficiency. The RCM proceeded in the presence of Grubbs' Ru-complex, providing a new effective synthetic route to these natural products.     

Total synthesis of macrosphelides A, B, and E: first application of ring-closing metathesis for macrosphelide synthesis

A new synthetic route for macrosphelides A, B, and E based on ring-closing metathesis (RCM) was established. The substrates for RCM could be synthesized starting from commercially available chiral materials, methyl (S)-lactate and methyl (S)- or (R)-3-hydroxybutyrate, in good overall yields. In the investigation of the key RCM step, it was found that the steric factor around the reaction site significantly affected the reaction rate of macrocyclization. A detailed account regarding this synthetic study is described herein.     

Furan ring opening-isochromene ring closure: a new approach to isochromene ring synthesis

A new approach toward the synthesis of 1H-isochromenes based on the recyclization of the furan ring in the corresponding ortho-hydroxymethylbenzylfurans is described.     

Enantioselective total synthesis of macrosphelides A and E

Enantioselective synthesis of 16-membered trilactone macrolides, macrosphelide A and E from (S)-lactic acid is described. Key features of the synthesis include the utility of a hitherto unexplored β-ketophosphonate derived from lactic acid and Yamaguchi lactonization leading to the title compounds.     

Furan ring opening—indole ring closure: pseudooxidative furan ring opening in the synthesis of indoles

A new approach to the synthesis of 4-(2-indolyl)-3-buten-2-ones is described based on condensation of 2-tosylaminobenzyl alcohols with N-tosylfurfurylamine. Pseudooxidative furan ring opening occurred via protolytic elimination of tosylamide from the side chain of the 2-tosylaminoaryl(5-tosylaminomethylfur-2-yl)methanes formed in situ.     

RCM mediated synthesis of macrosphelides I and G

The total synthesis of 16-membered macrolides, macraosphelides I and G, has been achieved starting from ethyl-(S)-lactate and (S)-malic acid. A combination of Jacobsen’s hydrolytic kinetic resolution and Sharpless epoxidation is used for the creation of two stereogenic centres, while Yamaguchi esterification and ring-closing metathesis strategies were used for the construction of the lactone ring.     

A strategy for the synthesis of mesostructured metal oxides with lower oxidation states

A detailed study on the pseudomorphic conversion of ordered mesoporous Co(3)O(4) and ferrihydrite into CoO and Fe(3)O(4), respectively, by using alcohol/water vapor as a gentle reducing agent is described. The reduction conditions for the transformation were optimized. In addition, the first one-pot synthesis of mesostructured CoO by using nanocasting with cubic ordered silica as a hard template is demonstrated.     

First synthesis of the A/B ring of ouabain

[reaction: see text] The synthesis of the fully fuctionalized A/B ring of ouabain has been accomplished efficiently from commercially available starting materials. A key Robinson annulation allows for the building of the desired carbon framework in one high-yielding step. Directed epoxidation followed by selective epoxide opening furnished the final tetraol with the desired all-cis stereochemistry.     

The oxidation of organocuprates--an offbeat strategy for synthesis

The creation of carbon-carbon and carbon-heteroatom bonds by the oxidation of organocuprates is useful in a range of challenging contexts including the formation of biaryl bonds within medium rings, diene synthesis and the coupling of tertiary carbon centres. This tutorial review introduces these applications and recent developments which have served to improve its functional group tolerance and its utility in organic synthesis.     

A highly efficient synthesis of the hemibrevetoxin B ring system

[reaction: see text] This Letter describes the synthesis of the hemibrevetoxin B tetracyclic ring system in 14 linear transformations from the Danishefsky-Kitahara diene.     

A strategy for the asymmetric synthesis of medium ring oxygen heterocycles: Enantioselective total synthesis of (+)-octahydrodeacetyldebromolaurencin

The asymmetric synthesis of the laurencin degradation product (2) by methylenation of the chiral heptanolide (5), conformationally controlled hydroboration of the enol ether (6), to give exclusively the cis-alcohol (7), and introduction of the pentyl side chain, demonstrates a new approach to the enantioselective synthesis of 2,8-disubstituted oxocanes, and confirms the absolute configuration of laurencin (1).     

A strategy for the total synthesis of dragmacidin E. Construction of the core ring system

[reaction: see text] The construction of the dragmacidin core ring system by a route that features the application of a new indole annelation reaction sequence is described.     

Convergent synthesis of the E'FGH ring fragment of ciguatoxin 1B via an acetylene cobalt complex strategy

A convergent synthesis of the E'FGH ring fragment 28 of ciguatoxin 1B, a principal toxin causing widespread seafood poisonings "ciguatera", has been accomplished through (i) coupling between the E' ring-acetylide 9 and the H ring-aldehyde 20, (ii) stereoselective F ring cyclization via an acetylene cobalt complex, (iii) conversion to a carbonyl function under high-pressure hydrogenation, and (iv) reductive hydroxyketone cyclization to construct the G ring. In the (1)H NMR analysis of 28 at room temperature, a considerable broadening phenomenon was observed due to the slow conformational changes of the FG ring, as reported for natural ciguatoxin 1B. When measured in pyridine at -20 degrees C, the spectra of 28 exhibited a 3.5:1 mixture of two conformational isomers (UP and DOWN conformers).     

Convergent synthesis of the E'FGH' ring fragment of ciguatoxin 1B via an acetylene cobalt complex strategy

[reaction: see text] A convergent synthesis of the E'FGH' ring fragment of ciguatoxin has been accomplished through (i) coupling between the E' ring-acetylide and the H' ring-aldehyde, (ii) stereoselective F ring cyclization via an acetylene cobalt complex, (iii) conversion to a carbonyl function, and (iv) reductive hydroxy-ketone cyclization to construct the G ring.     

Syntheses of aza-analogues of macrosphelides via RCM strategy and their biological evaluation

Syntheses of 16-membered macrolactams, which were aza-analogues of macrosphelides, could be established effectively by a ring-closing metathesis (RCM) strategy. Novel 19 analogues and six aza-macrosphelide-epothilone hybrids were furnished according to simple operations. Biological assay of these artificial aza-macrosphelides revealed that some of them showed stronger apoptosis-inducing activity against human lymphoma cells than the parent compound.     

A novel strategy for bioconjugation: synthesis and preliminary evaluation with amphotericin B

A novel linker strategy is presented based on a double reductive amination of a dialdehyde to the amine of the amphotericin B mycosamine sugar and the biological activity of a series of conjugates is compared to the native amphotericin B.     

A ring-closing metathesis approach to a synthesis of the B ring of eleutherobin

A short and efficient RCM route is reported for the construction of the key nine-membered B ring of eleutherobin starting from the readily available 1,2,5,6-diisopropylidene-d-glucose.     

Concomitant ring contraction cyclization strategy for the synthesis of novel 4-oxo-4,5-dihydro-pyrroloquinolines

The synthesis of novel substituted pyrroloquinolinones is described by concomitant ring contraction cyclization form 2-(2-amino-5-nitro-phenyl)-[4H]-1,3-thiazines, which were derived from N-substituted 5-nitro-anthranilonitrile. An easy access to novel 4-thiono-1,4-dihydro-1,3-quinazoline heterocycles is also mentioned.     

A novel cyclization/oxidation strategy for a two-step synthesis of (Z)-aurone

An efficient and facile two-step strategy for the synthesis of (Z)-aurone from arylacetylenes and salicyladehydes, via silver(I) nitrate mediated cyclization/oxidation in the presence of potassium carbonate has been developed. The key feature of our method was delicate cascade reaction, to provide the corresponding (Z)-aurone in high yield and good regio- and stereo selectivity.