Synthetic studies and biosynthetic speculation on marine alkaloid chartelline

Synthetic studies and biosynthetic speculation on chartelline inspired by an unexpected reaction are described.     

A novel synthetic approach to fluorine-containing acetylenic compounds based on Nicholas reaction

The fluorine-containing dicobalthexacarbonyl complex, prepared readily from γ-fluoroalkylated propargyl acetates and Co₂(CO)₈, reacted smoothly with various nucleophiles at the propargylic position, followed by oxidative decomplexation under the influence of Fe(NO₃)₃, to afford fluoroalkylated alkynes bearing various types of alkyl side chains in good to high yields.     

A synthetic approach to enfumafungin

The stereospecific synthesis of the dienophile subunits 5 was achieved from the butenolide 6. Ester 19 was obtained in 67% overall yield (2 steps), with no intermediate purification, by a sodium chlorite oxidation of the corresponding aldehyde in buffered conditions, followed immediately after extraction, by a Mitsunobu reaction of the relatively labile acid 3 with alcohol 13. The synthesis of the α,β-unsaturated aldehydes 22 and 23 is also reported. Tentative IMDA reactions of 22 and 23 were examined in thermal conditions, or with a Lewis acid catalysis, and results are reported herein.     

A new synthetic approach to phosphatidylethanolamine

A new synthetic method for phosphatidylethanolamine head group was developed via ring-opening of cyclic dioxaphospholane 2 with sodium azide and subsequent hydrogenation.The advantage of this strategy included short reaction steps,readily available materials and good yields.     

A new synthetic approach to benzomorphans

A new approach to the synthesis of benzomorphan derivatives is exemplified by the obtention of 3,6-dimethyl-benzomorphan from the readily available 1-methyl-2,3-benzobicyclo-[3,2,l]octane-4,6-dione.     

A diversity-oriented synthetic approach to bengamides

A new approach to the bengamides, a new class of antitumor natural products of marine origin, is reported from epoxyamides, prepared by reaction of aldehydes with sulfur ylides. The synthetic strategy has been designed for the delivery of a wide array of analogues. Thus, the terminal alkyl substituent is introduced by a cross olefin metathesis from the corresponding terminal olefin. The combination of cross olefin metathesis, introduction of different nucleophiles by the oxirane ring opening and the introduction of different amines via amide bond formation, can produce a wide array of bengamides analogues.     

A new synthetic approach to 7-hydroxynitidine

Benzo[c]phenanthridine alkaloid, 7-hydroxynitidine, was synthesized from readily available 2-benzyloxy-6-bromo-3,4-dimethoxybenzaldehyde 5 and napthylamine 6 using reductive amination followed by radical cyclization in eight steps. This method is highly efficient and better way to synthesize fully aromatized benzo[c]phenanthridine compounds.     

A synthetic approach to the trichothecene deoxynivalenol

Progress towards the total synthesis of deoxynivalenol (8) is described, leading to the advanced intermediate (25). Notable steps include a facile allyl alcohol epimerisation, a regioselective reductive deoxygenation, and a highly stereoselective Claisen allyl enol ether rearrangement.     

A convenient synthetic approach to bis-functionalised quaterfluorenes

Ni(COD)₂ promoted coupling of bromofluorenes functionalised with boronic esters or trimethylsilyl groups proves to be an efficient method for the preparation of reactive bifluorenes, which are key intermediates for the synthesis of bis-substituted oligofluorenes. The synthetic method has been exploited as a key step for the synthesis of a chiral 2,7?-diiodo-quaterfluorene and a 2,7?-bis-amino quaterfluorene.     

A unified synthetic strategy toward oroidin-derived alkaloids premised on a biosynthetic proposal

Details of the evolution of a synthetic strategy toward the spirocyclic chlorocyclopentane core of oroidin-derived alkaloids, including the axinellamines and potentially adaptable to palau'amine, are described. A proposed refinement of the Kinnel-Scheuer biosynthetic proposal for palau'amine is posited. Studies undertaken to improve the regioselectivity and efficiency of a key Diels-Alder reaction utilizing a novel protecting group strategy, microwave chemistry, and other strategies are described. Further insights regarding the suitability of different protecting groups during the epoxidation/chlorination/ring contraction sequence are disclosed. Several interesting by-products from this reaction sequence are reported. These studies have led to a unified synthetic strategy to the axinellamines and palau'amine.     

A synthetic approach to nomofungin/communesin B

[reaction: see text] A highly stereoselective intramolecular cycloaddition of an indole tethered to an aza-ortho-xylylene intermediate effects the rapid construction of a substantial portion of the ring system of the cytotoxic natural product communesin B. An analogous cycloaddition involving an ortho-quinone methide intermediate provides an adduct that clearly revealed that the structural assignment for nomofungin was in error.     

A unified synthetic approach to the pyrazinone dragmacidins

This review describes recent developments from our laboratory involving the synthesis of the structurally complex, pyrazinone-containing dragmacidin alkaloids.