Convergent Formal Synthesis of Ecteinascidin 743

Formal Synthesis of Ecteinascidin 743 from N-Cbz-l-tyrosine

A formal total synthesis of ecteinascidin 743 and lurbinectedin is achieved. Key features involve a Pictet-Spengler cyclization coupling of the tetrahydroisoquinoline and phenylalaninol moieties prepared by a common route with high yield and selectivity, a Parikh-Doering oxidation with good chemoselectivity and functionality tolerance, and a light-mediated A-ring elaboration of pentacyclic methoxyquinone substrates. By the approach, the known advanced intermediate (4-step conversion to Et-743) can be obtained conveniently in 21 total steps from N-Cbz-l-tyrosine.

Enantioselective Total Synthesis of (+)-Penostatins A and C

A stereoselective and column-economic approach to (+)-penostatins A and C has been developed. The multisubstituted A ring and B/C rings in their unique tricyclic framework are constructed through a Diels-Alder reaction/ozonolysis sequence and an exo intramolecular hetero-Diels-Alder reaction with high chemo-, regio-, and stereoselectivity. Using this route, (+)-penostatins A and C can be synthesized in 19 and 20 steps, respectively, with a good overall yield involving only five or six column chromatographic purifications.

Formal Synthesis of Ecteinascidin 743 via an Intramolecular Cascade Heck Reaction to Construct the Diazabicyclo[3.3.1]nonane Framework

A synthetic route to ecteinascidin 743 has been established via an intramolecular cascade Heck reaction to construct the diazabicyclo[3.3.1]nonane skeleton while controlling the two contiguous stereogenic centers. The strategically formed five-membered ring was oxidatively cleaved to generate a dialdehyde intermediate, from which the B ring of ecteinascidin 743 was constructed.

A Synthetic Approach to Several C7-Carbasugars via a Key Intramolecular Morita-Baylis-Hillman Reaction

A new synthetic strategy for C7-carbasugars is developed via an intramolecular Morita-Baylis-Hillman reaction, in which a substituted dial precursor prepared from d-mannose cyclizes smoothly in the presence of DMAP to afford polyhydroxylated cyclohex-1-enecarbaldehyde with good yield. By employment of the cyclization products as key intermediates, the first syntheses of carbasugar ester 1 and epicorepoxydon A, as well as practical syntheses of epoxydines B and C, (-)-MK7607, (-)-streptol, and (-)-gabosine E are achieved.

Total synthesis of the isoquinolinium metabolite ETM-204 of Trabectidin

Ecteinascidin-743 (Trabectidin, Trabectedin®, Yondelis®) is a synthetically obtained pharmaceutical drug originally isolated from a marine tunicate. Trabectedin is used for the chemotherapy of soft-tissue sarcoma and ovarian cancer. The isoquinolinium metabolite ETM-204 has been found in biotransformation and degradation studies of Trabectedin. We report the first total synthesis of ETM-204 and its full spectroscopic characterization confirming the postulated structure. Central elements of the 12-step synthesis starting from 2-methyl-6-nitrophenol are a Cu-mediated conversion of an iodoarene to a phenol, a Skattebøl-formylation, and a modified Pomeranz–Fritsch cyclization to assemble the isoquinoline ring. The pH-dependence of its visual absorbance could be clarified.

Graphic abstract

Total Synthesis of (-)-Lepadin F based on a Stereoselective Diels-Alder Reaction Controlled by a Ketolactone-type Dienophile

An efficient approach to the type III lepadin alkaloids (lepadins F and G) has been developed through a key Diels-Alder reaction, in which a novel ketolactone-type dienophile with chiral diol unit is employed to generate the desirable all-cis-trisubstituted cyclohexene with excellent regio- and stereoselectivity control. The subsequent selective sulfonylation of the diol unit followed by S_N 2 cyclization under hydrogenation conditions could construct the substituted piperidine ring. By using this approach, (-)-lepadin F is synthesized from ethyl l-lactate for the first time.

Recent progress toward the asymmetric synthesis of carbon-substituted piperazine pharmacophores and oxidative related heterocycles

The piperazine drugs are mostly N-substituted compared to only a few C-substituted drugs. To explore this unknown chemical space, asymmetric syntheses of C-substituted piperazines is the subject of this review.

The important requirement for approval of a new drug, in case it happens to be chiral, is that both enantiomers of the drug should be studied in detail, which has led synthetic organic and medicinal chemists to focus their attention on the development of new methods for asymmetric synthesis especially of relevant saturated N-heterocycles. On the other hand, the piperazine ring, besides defining a major class of saturated N-heterocycles, has been classified as a privileged structure in medicinal chemistry, since it is more than frequently found in biologically active compounds including several marketed blockbuster drugs such as Glivec (imatinib) and Viagra (sildenafil). Indeed, 13 of the 200 best-selling small molecule drugs in 2012 contained a piperazine ring. Nevertheless, analysis of the piperazine substitution pattern reveals a lack of structural diversity, with almost every single drug in this category (83%) containing a substituent at both the N1- and N4-positions compared to a few drugs having a substituent at any other position (C2, C3, C5, and C6). Significant chemical space that is closely related to that known to be biologically relevant, therefore, remains unexplored. In order to explore this chemical space, efficient and asymmetric syntheses of carbon-substituted piperazines and related heterocycles must be designed and developed. Initial, recent efforts toward the implementation of this particular target are in fact the subject of this review.