Straightforward Stereoselective Synthesis of Seven-Membered Oxa-Bridged Rings through In Situ Generated Cycloheptenol Derivatives

An iodine-mediated stereoselective synthesis of seven-membered oxa-bridged rings via in situ generated cycloheptenols was reported. This process was realized through the combination of C-C σ-bond cleavage and C-O bond-forming reactions in a one-pot fashion from simple and easily accessible raw materials. The formation of carbon radicals initiated by I₂ was the key to the reaction.

Construction of key building blocks towards the synthesis of cortistatins

This work reports the construction of key building blocks towards the synthesis of cortistatins; a family of steroidal alkaloids. Cortistatin A, being a primary target due to its superior biological properties over other congeners, has been prepared by two different synthetic routes. Synthesis of the precursor to the heavily substituted A-ring starting from d-glucose and construction of the DE-ring junction employing a Hajos-Parrish ketone as a chiral pool have been demonstrated. Efforts are underway to assemble these key fragments and build towards the total synthesis of cortistatin A.

Synthetic Study toward Total Synthesis of (±)-Germine: Synthesis of (±)-4-Methylenegermine

The total synthesis of 4-methylenegermine is described.

Constructing molecular complexity and diversity: total synthesis of natural products of biological and medicinal importance

The advent of organic synthesis and the understanding of the molecule as they occurred in the nineteenth century and were refined in the twentieth century constitute two of the most profound scientific developments of all time. These discoveries set in motion a revolution that shaped the landscape of the molecular sciences and changed the world. Organic synthesis played a major role in this revolution through its ability to construct the molecules of the living world and others like them whose primary element is carbon. Although the early beginnings of organic synthesis came about serendipitously, organic chemists quickly recognized its potential and moved decisively to advance and exploit it in myriad ways for the benefit of mankind. Indeed, from the early days of the synthesis of urea and the construction of the first carbon-carbon bond, the art of organic synthesis improved to impressively high levels of sophistication. Through its practice, today chemists can synthesize organic molecules--natural and designed--of all types of structural motifs and for all intents and purposes. The endeavor of constructing natural products--the organic molecules of nature--is justly called both a creative art and an exact science. Often called simply total synthesis, the replication of nature's molecules in the laboratory reflects and symbolizes the state of the art of synthesis in general. In the last few decades a surge in total synthesis endeavors around the world led to a remarkable collection of achievements that covers a wide ranging landscape of molecular complexity and diversity. In this article, we present highlights of some of our contributions in the field of total synthesis of natural products of biological and medicinal importance. For perspective, we also provide a listing of selected examples of additional natural products synthesized in other laboratories around the world over the last few years.

Synthetic studies toward (+)-cortistatin A

We describe herein the synthesis of a late-stage intermediate en route to cortistatin A. Key transformations included a Snieckus-like cascade sequence culminating in a 6π-electrocyclization, an alkylative dearomatization, and the stereoselective functionalization of the cortistatin A-ring. While the total synthesis we sought was not accomplished, the work sets the stage for several approaches to the preparation of novel analogs via diverted total synthesis.

Total synthesis of (±)-cortistatin J from furan

A concise, diastereoselective total synthesis of (±)-cortistatin J has been completed in 20 steps from furan. Key steps include an intramolecular [4 + 3] cyclization of a disubstituted furan with a (Z)-2-(trialkylsilyloxy)-2-enal to construct the tetracyclic core and a (Z)-vinylsilane/iminium ion cyclization to form the A ring.

Stereoselective synthesis of core structure of cortistatin A

A stereoselective synthesis of the core structure of cortistatin A (1), a novel antiangiogenic steroidal alkaloid from Indonesian marine sponge, is described. An 8-oxabicyclo[3.2.1]octene system, a characteristic B-ring structure of 1, was elaborated by a 7-endo selective intramolecular Heck cyclization and a subsequent acid-mediated oxy-Michael reaction.

Scalable synthesis of cortistatin A and related structures

Full details are provided for an improved synthesis of cortistatin A and related structures as well as the underlying logic and evolution of strategy. The highly functionalized cortistatin A-ring embedded with a key heteroadamantane was synthesized by a simple and scalable five-step sequence. A chemoselective, tandem geminal dihalogenation of an unactivated methyl group, a reductive fragmentation/trapping/elimination of a bromocyclopropane, and a facile chemoselective etherification reaction afforded the cortistatin A core, dubbed "cortistatinone". A selective Δ(16)-alkene reduction with Raney Ni provided cortistatin A. With this scalable and practical route, copious quantities of cortistatinone, Δ(16)-cortistatin A (the equipotent direct precursor to cortistatin A), and its related analogues were prepared for further biological studies.

Concise synthesis of the oxapentacyclic core of cortistatin A

A concise synthetic approach for constructing the oxapentacyclic framework of cortistatin A is described. The synthesis features a furan-oxyallyl [4 + 3] cycloaddition and double-intramolecular aldol reactions. In addition, an interesting core structure was obtained in 11 steps from furan by using our method.

Synthesis of cortistatins A, J, K and L

The cortistatins are a recently identified class of marine natural products characterized by an unusual steroidal skeleton, which have been found to inhibit differentially the proliferation of various mammalian cells in culture by an unknown mechanism. We describe a comprehensive route for the synthesis of cortistatins from a common precursor, which in turn is assembled from two fragments of similar structural complexity. Cortistatins A and J, and for the first time K and L, have been synthesized in parallel processes from like intermediates prepared from a single compound. With the identification of facile laboratory transformations linking intermediates in the cortistatin L synthetic series with corresponding intermediates to cortistatins A and J, we have been led to speculate that somewhat related paths might occur in nature, offering potential sequencing and chemical detail for cortistatin biosynthetic pathways.

Formal total synthesis of (±)-cortistatin A

A second-generation synthesis of the pentacyclic core of the cortistatins, a family of rearranged steroidal alkaloids that have recently attracted much attention, is reported. The improved sequence provides access to significant quantities of this key compound, which enabled a formal total synthesis of (±)-cortistatin A by conversion to the key Nicolaou/Hirama dienone. It is anticipated that this new, robust route to the pentacyclic core will facilitate the total synthesis of a range of natural products in the cortistatin family, as well as the construction of key structural analogs to probe the promising biological activity of these important compounds.

Fused bicyclic piperidines and dihydropyridines by dearomatising cyclisation of the enolates of nicotinyl-substituted esters and ketones

The silyl enol ether derivatives of ketones or esters tethered by a hydrocarbon or ether linkage to the 3-position of a pyridine ring undergo dearomatising nucleophilic attack on the ring once it is activated (as an acylpyridinium species) by the addition of methyl chloroformate. The bicyclic dihydropyridine products are in some cases unstable, but may be isolated after hydrogenation as fused bicyclic piperidines.

A hypervalent iodine-induced double annulation enables a concise synthesis of the pentacyclic core structure of the cortistatins

A stereocontrolled synthesis of a complex pentacycle embodying the molecular architecture of the cortistatin class of natural products was achieved from the (+)-Hajos-Parrish ketone. The cornerstone of our approach is a hypervalent iodine induced tandem intramolecular oxidative dearomatization and nitrile oxide cycloaddition. The manner in which these ring formations were orchestrated has yielded a rather concise strategy for synthesis.

Stereodivergent synthesis of 17-alpha and 17-beta-alpharyl steroids: application and biological evaluation of D-ring cortistatin analogues

One stereocenter makes all the difference: The synthesis and biological evaluation of 17-epi-cortistatin A is reported from a common intermediate used to procure natural cortistatin A. The synthesis features a unique stereocontrolled Raney-Ni reduction process that can be employed to reliably produce both alpha- and beta-configured D-ring aryl steroids. Biological evaluations of these "cortalogs" are reported for the first time.