Stereocontrolled synthesis of cytotoxic anhydrosphingosine pachastrissamine by using [3.3] sigmatropic rearrangement of allyl cyanate

Design, synthesis and evaluation of bioactivity of peptidomimetics based on chloroalkene dipeptide isosteres

Ample biologically active peptides have been found, identified and modified for use in drug discovery to date. However, several factors, such as low metabolic stability due to proteolysis and non-specific interactions with multiple off-target molecules, might limit the therapeutic use of peptides. To enhance the stability and/or bioactivity of peptides, the development of "peptidomimetics," which mimick peptide molecules, is considered to be idealistic. Hence, chloroalkene dipeptide isosteres (CADIs) was designed, and their synthetic methods have been developed by us. Briefly, in a CADI an amide bond in peptides is replaced with a chloroalkene structure. CADIs might be superior mimetics of amide bonds because the Van der Waals radii (VDR) and the electronegativity value of a chlorine atom are close to those of the replaced oxygen atom. By a developed method of the "liner synthesis", N-tert-butylsulfonyl protected CADIs can be synthesized via a key reaction involving diastereoselective allylic alkylation using organocopper reagents. On the other hand, by a developed method of the "convergent synthesis", N-fluorenylmethoxycarbonyl (Fmoc)-protected carboxylic acids can be also constructed based on N- and C-terminal analogues from corresponding amino acid starting materials via an Evans syn aldol reaction and the Ichikawa allylcyanate rearrangement reaction involving a [3.3] sigmatropic rearrangement. Notably, CADIs can also be applied for Fmoc-based solid-phase peptide synthesis and therefore introduced into bioactive peptides including as the Arg-Gly-Asp (RGD) peptide and the amyloid β fragment Lys-Leu-Val-Phe-Phe (KLVFF) peptide, which are correlated with cell attachment and Alzheimer's disease (AD), respectively. These CADI-containing peptidomimetics stabilized the conformation and enhanced the potency of the cyclic RGD peptide and the cyclic KLVFF peptide.

First synthesis of (±)-halichonadins A-D

Described herein is the first total synthesis of a marine isocyanide terpene, (±)-halichonadin C. Our synthetic strategy features nitrile-to-isocyanide interconversion utilizing hypervalent iodine-promoted Hofmann rearrangement. This approach led to successful construction of an isocyanide group at the stereochemically encumbered C-6 position in (±)-halichonadin C. Furthermore, in accord with a scenario we propose for the biosynthesis of halichonadins A-D, (±)-halichonadin C was transformed to halichonadins A and B via the missing link intermediate, halichonadin isocyanate.

Flow Pd(II)-Catalysed Carbonylative Cyclisation in the Total Synthesis of Jaspine B

This work describes the total synthesis of jaspine B involving the highly diastereoselective Pd(II)-catalysed carbonylative cyclisation in the preparation of crucial intermediates. New conditions for this transformation were developed and involved the pBQ/LiCl as a reoxidation system and Fe(CO)5 as an in situ source of stoichiometric amount of carbon monoxide (1.5 molar equivalent). In addition, we have demonstrated the use of a flow reactor adopting proposed conditions in the large-scale preparation of key lactones.

Synthetic analogues of marine cytotoxic jaspine B and its stereoisomers

Synthetic analogues of the cytotoxic jaspine B and its stereochemical congeners have become an attractive target in the synthetic organic community owing to the search for novel therapeutic candidates with more potent anticancer activity, as cancer is the second leading cause of death worldwide. This review article provides insights into the different approaches and strategies available in the literature for the construction of jaspine B-related compounds.

Synthetic Studies on a Pachastrissamine Sulfur Analogue: Synthesis of a 4-epi-Sulfur Analogue

A versatile synthetic procedure for a sulfur analogue of pachastrissamine (jaspine B), which involves the tandem thiolation-cyclization of a 1,4-ditosylate to construct a tetrahydrothiophene ring, was developed. Nucleophilic amino substitution of a tetrahydrothiophene-4-sulfonate with unexpected retention of the configuration afforded the sulfur analogue of 4-epi-pachastrissamine.

Practical Synthesis of Pachastrissamine (Jaspine B), 2-epi-Pachastrissamine, and the 2-epi-Pyrrolidine Analogue

The practical syntheses of pachastrissamine (jaspine B), 2-epi-pachastrissamine, and the 2-epimer of the pyrrolidine analogue were accomplished via the stereoselective reduction of an allylketone derived from commercially available diethyl D-tartrate and the cross-metathesis of an allyltetrahydrofuran or allypyrrolidine with 1-tridecene as key steps.

Formation of tetrahydrofurans via a 5-endo-tet cyclization of aziridines--synthesis of (-)-pachastrissamine

The formation of tetrahydrofurans from 2-hydroxyalkyl-oxirane or aziridine is reported. The 5-endo-tet cyclization/ring opening of aziridine proceeded smoothly to give tetrahydrofurans (THFs) under mild conditions. In contrast, the corresponding process of oxirane was unsuccessful and a sequence of SN2 substitution/cyclization was required to form THFs. The application of the process to prepare ent-(-)-pachastrissamine is described.

Stereodivergent synthesis of jaspine B and its isomers using a carbohydrate-derived alkoxyallene as C3-building block

Herein we present the synthesis of the anhydrophytosphingosine jaspine B and three of its stereoisomers using a carbohydrate-derived alkoxyallene in order to obtain the products in enantiopure form. Key step of the reaction sequence is the addition of the lithiated alkoxyallene to pentadecanal, setting the configuration at the later C-2 of the ring system. This reaction step proceeds with moderate selectivity and therefore leads to a stereodivergent approach to the natural product and its enantiomer. The gold-catalyzed 5-endo-cyclization affords the corresponding dihydrofurans, which after separation, azidation of the enol ether moiety and two subsequent reduction steps give the natural product and its stereoisomers.

Asymmetric synthesis of Pachastrissamine (Jaspine B) and its diastereomers via η3-allylpalladium intermediates

A short route for the synthesis of Pachastrissamine (Jaspine B), an anhydrosphingosine derivative, and all three of its diastereomers is presented. The route consists of only 9 steps from the commercially available Garner's aldehyde. The furan framework is formed via an η(3)-allylpalladium intermediate.

Ring-construction/stereoselective functionalization cascade: total synthesis of pachastrissamine (jaspine B) through palladium-catalyzed bis-cyclization of propargyl chlorides and carbonates

Palladium(0)-catalyzed cyclization of bromoallenes, propargyl chlorides, and carbonates bearing hydroxy and benzamide groups as internal nucleophiles stereoselectively provides functionalized tetrahydrofuran. Cyclization reactivity is dependent on the relative configuration of the benzamide and leaving groups, and on the nature of the leaving groups. This bis-cyclization was used as the key step in a short total synthesis of pachastrissamine, which is a biologically active marine natural product.