Model studies for the total synthesis of the maytansinoids based on the intramolecular nitrile oxide-olefin [3+2] cycloaddition reaction

Remote Stereoinductive Intramolecular Nitrile Oxide Cycloaddition: Asymmetric Total Synthesis and Structure Revision of (-)-11β-Hydroxycurvularin

The first total synthesis and structure revision of (-)-11β-hydroxycurvularin (1b), a macrolide possessing a β-hydroxyketone moiety, were accomplished. The β-hydroxyketone moiety in this natural product was introduced by cleavage of the N-O bond in an isoxazoline ring that was formed diastereoselectively in a 1,5-remote stereocontrolled fashion by employing intramolecular nitrile oxide cycloaddition.

Synthesis and Intramolecular Nitrile Oxide Cycloaddition of 3,5‘-Ether-Linked Pseudooligosaccharide Derivatives: An Approach to Chiral Macrooxacycles

3,5'-ether-linked pseudooligopentose derivatives were synthesized for the first time from readily available carbohydrate precursors. The 1,2-isopropylidene-protected ether-linked oligopentoses are potentially important as precursors of novel RNA analogues. Intramolecular cycloaddition of the nitrile oxides prepared from these derivatives led to the diastereoselective formation of chiral isoxazolines fused to 10-16-membered oxacycles. The stereochemistry of some of these isoxazolines was established by X-ray diffraction and NOESY analysis.

Recent Developments in the Maytansinoid Antitumor Agents

Maytansine and its congeners have been isolated from higher plants, mosses and from an Actinomycete, Actinosynnema pretiosum. Many of these compounds are antitumor agents of extraordinary potency, yet phase II clinical trials with maytansine proved disappointing. The chemistry and biology of maytansinoids has been reviewed repeatedly in the late 1970s and early 1980s; the present review covers new developments in this field during the last two decades. These include the use of maytansinoids as "warheads" in tumor-specific antibodies, preliminary metabolism studies, investigations of their biosynthesis at the biochemical and genetic level, and ecological issues related to the occurrence of such typical microbial metabolites in higher plants.

A preliminary approach to nonenolizable beta,beta-tricarbonyls: assembly of a hyperevolutin prototype

A synthetic approach to the hyperevolutin A acylated phloroglucinol ring system is described. Thus, intramolecular allene-nitrile oxide cycloaddition of 10 was used to construct the bicyclic framework and vicinal quaternary centers in cycloadduct 20 in the key bond-forming step. Treatment of 20 with Raney nickel and hydrogen gas produced primary enamine 21 which contains a nonenolizable beta,beta-tricarbonyl group in latent form.