Synthesis of marine sponge alkaloid hachijodine B and a comment on the structure of ikimine B and on the absolute configuration of niphatesine D

The syntheses of the proposed structures of hachijodine B 1, ikimine B 2 and niphatesine D 3 from S-citronellol are described. Our results suggest that the gross structures of hachijodine B and niphatesine D are correct, but that ikimine B was incorrectly assigned. We have also established that the previous absolute stereochemical assignment for niphatesine D is unreliable.     

Studies toward the total synthesis of the cytotoxic sponge alkaloid pyrinodemin A

[structure: see text]. The syntheses of the proposed structure of pyrinodemin A (1) and its cis double bond positional isomer (C15'-C16') in racemic form are described. The key reaction involved an intramolecular nitrone/double bond cycloaddition. Our results suggest that neither 1 nor its double positional isomer is the correct structure of pyrinodemin A     

A simple approach for the synthesis of azocine alkaloids: The total synthesis of megallanesine

A new three step synthetic route to construct azocine ring system using anion chemistry and intramolecular Friedel-Craft reaction of an ester is presented. This method allows synthesis of azocine ring analogues in excellent overall yields. The designed strategy was applied for the synthesis of naturally occurring magallanesine.     

A new synthesis of the phytotoxin porritoxin

A convenient synthesis of the phytotoxin porritoxin is described. Central to the approach employed is the formation of the isoindolinone template obtained via a directed lithiation/Parham cyclization process enabling the concomitant connection of an acetal appendage. Further conversion into the requisite hydroxyalkyl chain, selective deprotection, and O-prenylation complete the synthesis of the title compound.     

A new approach to isoindoloisoquinolinones. A simple synthesis of nuevamine

A convenient and versatile short step synthesis of isoindoloisoquinolinones, illustrated by the total synthesis of the alkaloid nuevamine 1a, is described. The tetracyclic lactam compounds were obtained by a tactical combination of the Parham procedure for the elaboration of the isoindolinone template and an aryne-mediated cyclization giving rise to the nitrogen containing six-membered heteroring unit.     

Asymmetric synthesis of cytotoxic sponge metabolites R-strongylodiols A and B

The asymmetric synthesis of the marine sponge natural products, R-strongylodiols A 1 and B 2 using a minimum protection strategy is described. The chirality of the natural products was introduced via the Noyori asymmetric reduction of ynones.     

Intramolecular Diels-Alder reaction of 1-aminoisobenzofurans: Application to the synthesis of benzo[c]phenanthridines

Intramolecular Diels-Alder reactions of 1-aminoisobenzofurans give benzo[c]phenanthridines. The reactive intermediates are generated from o-(diazomethyl)benzamides.     

A concise benzotriazolyl-mediated synthesis of 9-methoxycepharanone A

A concise synthesis of 9-methoxycepharanone A is described. The key step is the benzotriazolyl-assisted assemblage of an arylmethyleneisoindolinone ring system comprising the enol ether unit. Radical cyclization followed by deprotections and ultimate formation of the methylenedioxy group complete the total synthesis of the title compound.     

Concise synthesis of 1-epi-castanospermine

1-epi-Castanospermine (5) was synthesized from readily available 2,3,4,6-tetra-O-benzyl-1-deoxynojirimycin (11) in 9 steps and 21% overall yield, with selective debenzylation, Barbier reaction and reductive amination as the main reaction steps.     

Two New Alkaloids from the Aerial Part of Peganum nigellastrum

Two new alkaloids, pegamine β‐D ‐glucopyranoside ( 1 ) and 2‐deoxypeganylacetic acid ( 2 ), together with the novel 3,4‐dihydro‐4‐hydroxynaphthalene‐2‐carboxylic acid ( 3 ), were isolated from the aerial part of Peganum nigellastrum. The structures of these compounds were elucidated on the basis of spectroscopic analyses, including 1D‐ and 2D‐NMR, and ESI‐MS/MS.     

The preparation and cycloaddition reaction of 1-sulfonyl-1-trifluoromethyl allenes

A series of 1-sulfonyl-1-trifluoromethyl allenes were prepared for the first time from commercial available 2-bromo-3,3,3-trifluoropropene. Cycloaddition reaction of these trifluoromethylated allenes with nitrones occured readily under mild conditions, giving the corresponding trifluoromethylated isoxazolidines in high yields.     

A brief total synthesis of fumaramidine

The first total synthesis of the alkaloid fumaramidine is reported. The synthetic tactics involve the sequential construction of the isoindolinone template by a Parham cyclization process followed by benzylic lactam deprotonation, interception with the suitable carboxaldehyde and ultimate E1cb elimination. Final N-lactam deprotection completes the synthesis of the Z configured title compound.     

TfOH catalyzed synthesis of 1-substituted tetrahydrocarbazoles

Synthesis of 1-substituted tetrahydrocarbazole is accomplished by TfOH catalyzed reaction of 3-substituted indoles tethered with secondary and tertiary alcohols. The reaction was generalized for a variety of substrates and was extended to the synthesis of 2,3,3a,6-tetrahydro-1H-pyrido[3,2,1-jk]carbazole and carbazoles.     

Annulation of pyrrole: application to the synthesis of indolizidine alkaloids

The nucleophilicity of pyrrole has been exploited to rapidly assemble the bicyclic skeleton of the indolizidine alkaloids. The key sequence is the annulation of a second ring onto pyrrole from a γ-lactone and has been exploited in the synthesis of the natural products (±)-monomorine and (±)-indolizidine 209D.     

The rational design of modified Cinchona alkaloid catalysts. Application to a new asymmetric synthesis of chiral chromanes

A new asymmetric synthesis of 2-substituted chiral chromanes has been achieved. The key step is the intramolecular conjugate addition of a phenolic nucleophile on a α,β-unsaturated ester catalyzed by Cinchona alkaloids. The high ee’s obtained with cinchonine and its derivatives have been rationalized by ab initio quantum chemistry calculations of transition state structures.     

Stereoselectivity in a nitroso-ene cyclization: Formal synthesis of rac-manzacidins A and C

Nitroso-ene (NE) reactions have been adapted in the construction of nitrogen-containing motifs in many biologically interesting compounds. The transient and highly reactive “nitroso” species remains a challenge for designing stereocontrolled syntheses. Although chiral auxiliary-based method has been developed to achieve high diastereoselectivity, the use of the inherent chirality of the nitroso compound for stereochemical control remains underdeveloped. We chose the formation of a γ-lactam via a NE cyclization as a basis to study the applicable principles for future asymmetric syntheses. The selected examples presented herein reveal that the intramolecular hydrogen bond would provide conformational restraint to facilitate excellent facial selectivity in the NE reaction via a chair-like transition state. The sterically bulky amino group also provides excellent stereochemical control possibly through steric repulsion. The following transformations led to a key intermediate (Ohfune's lactone) in the preparation of manzacidins A and C and thus constitutes a formal synthesis.     

Total synthesis of tryprostatins A and B

Three distinct synthetic routes to the 2-prenyl tryptophan core skeleton of tryprostatins and their total syntheses are described. The strategies include a traditional gramine-mediated coupling reaction, Fürstner indole synthesis, and our radical-mediated indole synthesis from o-alkenylphenyl isocyanide. The establishment of reliable conditions for the radical-mediated construction of indoles via a low-temperature radical initiator V-70 (2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile)) led to the highly efficient syntheses of tryprostatins A and B.