Total Synthesis and Structural Reassignment of Laingolide A

The asymmetric total synthesis of four diastereomers of laingolide A was achieved, which led to the unambiguous assignment of the stereochemistry of the natural product. The salient features of the convergent, fully stereocontrolled approach were a copper-catalysed stereospecific Kumada-type coupling, a Julia-Kocienski olefination and an RCM/alkene migration sequence to access the desired macrocyclic enamide.

Tertiary Enamides: Versatile and Available Substrates in Synthetic Chemistry

BACKGROUND

Enamines and their variant enamides as powerful and versatile synthons have attracted great attention in synthetic chemistry. Enamides display unique stability and reduce enaminic reactivity in view of the electron-withdrawing effect of N-acyl group. A great deal of satisfactory achievements in the synthesis and application of enamides has been made in recent years. Especially, tertiary enamides without N-H bond regarded as low reactivity of compounds in the past can act as excellent nucleophiles to react with electrophiles for the construction of various nitrous molecules.

OBJECTIVE

This review focuses on recent advances on tertiary enamides in the synthetic strategies and applications including addition, coupling reaction, functionalization and electro- or photo-chemical reaction.

CONCLUSION

Tertiary enamides as electron-deficient nucleophiles display a satisfactory balance between stability and reactivity to offer multiple opportunities for the construction of various functionalized nitrogencontaining compounds. Further exploration of the reactive mechanisms involved tertiary enamides and the development of novel and efficient transformations to generate ever more complex building blocks starting from tertiary enamides are particularly worth pursuing.

Total Synthesis of Laingolide B Stereoisomers and Assignment of Absolute Configuration

Total synthesis of (-)-(2 R,9 S)- and (+)-(2 S,9 S)-stereoisomers of laingolide B has been accomplished by using sequential ring-closing metathesis (RCM) and alkene isomerization to construct the macrocyclic trans- N-methyl enamide moiety. The Myers alkylation was used to secure the C2 stereochemistry of the two RCM precursors from a common (9 S)-C3-C9 alkyl iodide. The absolute configuration of laingolide B has been assigned as (2 S,9 R) by comparison of the optical rotation data.

One and Two-Carbon Homologation of Primary and Secondary Alcohols to Corresponding Carboxylic Esters Using β-Carbonyl BT Sulfones as a Common Intermediate

Herein we report the efficient one- and two-carbon homologation of 1° and 2° alcohols to their corresponding homologated esters via the Mitsunobu reaction using β-carbonyl benzothiazole (BT) sulfone intermediates. The one-carbon homologation approach uses standard Mitsunobu C-S bond formation, oxidation and subsequent alkylation, while the two-carbon homologation uses a less common C-C bond forming Mitsunobu reaction. In this latter case, the use of β-BT sulfone bearing esters lowers the p K_a sufficiently enough for the substrate to be used as a carbon-based nucleophile and deliver the homologated β-BT sulfone ester, and this superfluous sulfone group can then be cleaved. In this paper we describe several methods for the effective desulfonylation of BT sulfones and have developed methodology for one-pot alkylation-desulfonylation sequences. As such, overall, a one-carbon homologation sequence can be achieved in a two-pot (four step) procedure and the two-carbon homologation in a two-pot (three step) procedure (three-pot; four step when C-acid synthesis is included). This methodology has been applied to a wide variety of functionality (esters, silyl ethers, benzyls, heteroaryls, ketones, olefins and alkynes) and are all tolerated well providing good to very good overall yields. The power of our method was demonstrated in site-selective ingenol C20 allylic alcohol two-carbon homologation.

A facile approach for the synthesis of C13-C24 fragments of maltepolides A, C and D

A linear, chiron approach for the synthesis of C13-C24 fragments of cytostatic maltepolides A, C and D consisting of a tetrahydrofuran subunit and a chiral alkenyl/alkyl substituent is achieved from (+)-diethyl l-tartrate. The other chiral stereocenters were generated by employing key reactions such as Crimmins aldol, alkynylation and CeCl₃·7H₂O mediated Luche reduction reactions.

Synthesis and biological evaluation of palmyrolide A macrocycles as sodium channel blockers towards neuroprotection

Palmyrolide A is a neuroprotective macrolide isolated by Gerwick and coworkers in 2010. This natural product is known to suppress neuronal spontaneous calcium ion oscillations through its voltage-gated sodium channel blocking ability which is of significant interest in CNS drug discovery. Herein, we give a detailed account on total synthesis of (+)-palmyrolide A and synthesis of a focused library of macrocycles around the scaffold, followed by their biological evaluation. Use of the chiral pool approach, Zhu's oxidative homologation, access to unnatural cis-palmyrolide A, preparation of 18 new analogues and identification of macrolides with improved sodium channel blocking activity are the important features of the present paper. As a measure of potency as voltage-gated sodium channel blockers, all the synthesized analogues were profiled for their ability to inhibit the veratridine-stimulated Na(+) influx in murine primary neuronal cultures. Four macrocycles were found to be more potent or comparable to that of the natural product (-)-palmyrolide A. The most potent compound from this series 20 was structurally simplified and readily accessible in good quantities for further biological profiling.