Toward the total synthesis of spirastrellolide A. Part 3: intelligence gathering and preparation of a ring-expanded analogue.

Different methods for the formation of the C.25-C.26 bond of spirastrellolide A () are evaluated that might qualify for the end game of the projected total synthesis, with emphasis on metathetic ways to forge the macrocyclic frame.

Latrunculin analogues with improved biological profiles by "diverted total synthesis": preparation, evaluation, and computational analysis.

Deliberate digression from the blueprint of the total syntheses of latrunculin A (1) and latrunculin B (2) reported in the accompanying paper allowed for the preparation of a focused library of "latrunculin-like" compounds, in which all characteristic structural elements of these macrolides were subject to pertinent molecular editing. Although all previously reported derivatives of 1 and 2 were essentially devoid of any actin-binding capacity, the synthetic compounds presented herein remain fully functional. One of the designer molecules with a relaxed macrocyclic backbone, that is compound 44, even surpasses latrunculin B in its effect on actin while being much easier to prepare.

Total syntheses of the actin-binding macrolides latrunculin A, B, C, M, S and 16-epi-latrunculin B.

The latrunculins are highly selective actin-binding marine natural products and as such play an important role as probe molecules for chemical biology. A short, concise and largely catalysis-based approach to this family of bioactive macrolides is presented. Specifically, the macrocyclic skeletons of the targets were forged by ring-closing alkyne metathesis (RCAM) or enyne-yne metathesis of suitable diyne or enyne-yne precursors, respectively.

Diverted total synthesis: preparation of a focused library of latrunculin analogues and evaluation of their actin-binding properties.

Two largely catalysis-based and highly convergent total syntheses of latrunculin A (1) and B (2) were diverted to the preparation of a focused library of analogues of these potent actin-binding macrolides that enjoy widespread use in chemical biology. Because the chosen route allows for structural variations of all characteristic parts of the natural leads, it was possible to map the previously largely unknown structure/activity profile of this class of bioactive natural products. This led to the discovery that the removal of the methyl branches decorating the macrocycle in 2 engenders a significant increase in potency, while streamlining the synthesis to a considerable extent.

An asymmetric formal synthesis of fasicularin.

An asymmetric formal synthesis of fasicularin (1) is described. This natural product, isolated from the extracts of the marine invertebrate Nephteis fasicularis, has shown modest cytotoxicity towards Vero cells. Fasicularin is among only two members of the cylindricine family of natural products, along with lepadiformine (2), to possess a trans A-B ring junction.

Investigations of alpha-siloxy-epoxide ring expansions forming 1-azaspirocyclic ketones.

The construction of 1-azaspirocyclic cycloalkanones using a siloxy-epoxide semipinacol ring expansion process was examined. Functionalized 1-azaspiro[5.5]undecan-7-ones (1-azaspirocyclic cyclohexanones) proceeded in high chemical yields with complete diastereoselectivity using titanium tetrachloride as the Lewis acid promoter.

Synthesis of functionalized 1-azaspirocyclic cyclopentanones using bronsted acid or N-bromosuccinimide promoted ring expansions.

Azaspirocyclic ring systems are present in a variety of alkaloids. Functionalized 1-azaspirocyclopentanones (6, 7, 11, 12) can be efficiently constructed through semipinacol ring expansion reactions of 2-(1-hydroxycyclobutyl)-p-toluenesulfonylenamides (4) promoted by either a Bronsted acid ((S)-(+)-10-camphorsulfonic acid or HCl) or N-bromosuccinimide, an electrophilic bromine source. Reactions promoted by N-bromosuccinimide tend to proceed in higher yields (80-95%) and with greater diastereoselectivity (3:1-1:0) compared to those reactions promoted by a Bronsted acid.

A formal construction of fasicularin.

[reaction: see text] Our synthetic approach toward fasicularin is presented. Key steps in this construction are a siloxy-epoxide semipinacol rearrangement, a B-alkyl Suzuki reaction and an intramolecular S(N)2 reaction.