Total synthesis of (+/-)-halichlorine, (+/-)-pinnaic acid, and (+/-)-tauropinnaic acid.

The related marine natural products halichlorine, pinnaic acid, and tauropinnaic acid have been synthesized. The described route provided access to all three compounds from a common, late-stage intermediate. The synthesis began with 1-pyrrolidino-1-cyclopentene from which an intermediate possessing the three contiguous stereocenters of the natural products was synthesized in just four steps.

Synthesis of tricolorin F.

A hetero-trisaccharide resin glycoside of jalapinolic acid known as tricolorin F has been synthesized. The approach involved the preparation of intermediate 5 and a subsequent coupling reaction with imidate 6 to produce disaccharide 7, which after deacetylation generated intermediate 8. A further coupling between this glycosyl acceptor and the quinovose glycosyl donor 9 resulted in the formation of the tricoloric acid C derivative 10.

Multigram synthesis of the C29-C51 subunit and completion of the total synthesis of altohyrtin C (spongistatin 2).

A multigram synthesis of the C29-C51 subunit of altohyrtin C (spongistatin 2) has been accomplished. Union of this intermediate with the C1-C28 fragment and further elaboration furnished the natural product. Completion of the C29-C51 subunit began with the aldol coupling of the boron enolate derived from methyl ketone 8 and aldehyde 9.

A second-generation synthesis of the C1-C28 portion of the altohyrtins (spongistatins).

A practical second-generation synthesis of an advanced intermediate in our total synthesis of altohyrtin C (spongistatin 2) has been developed. A new approach to the C1-C15 (AB) portion features a vinyllithium addition to an aldehyde followed by a palladium-catalyzed allylic reduction to install the troublesome C13-C15 segment. Our general approach to the C16-C28 (CD) spiroketal has been retained, but some improvements have been made.

The pyridoacridine family tree: a useful scheme for designing synthesis and predicting undiscovered natural products.

The pyridoacridine natural products represent a large and growing class and serve here to illustrate the wealth of information that can be extracted by comparing natural products on the basis of structure and occurrence.

Oxidative fragmentation of pregna-14,16-dien-20-ones to 14 beta-hydroxyandrost-15-en-17-ones.

Two methods have been developed for efficient conversion of pregna-14,16-dien-20-ones into 14 beta-hydroxyandrost-15-en-17-ones. One procedure consists of treatment of the ring-D dienone successively with sodium borohydride and singlet oxygen. The reaction is illustrated by the conversion of pregna-14,16-dien-20-one 1 into 14 beta-hydroxyandrost-15-en-17-one 3, via the corresponding allylic alcohol 2.

A simple biomimetic synthesis of styelsamine B.

An extremely rapid, low cost, and environmentally friendly entry into the pyridoacridine family of alkaloids has been devised, as demonstrated here by the first total synthesis of styelsamine B (3) and its oxidation to the quinoneimine cystodytin J (4). The known reaction of cystodytin J with methanethiol makes this a formal synthesis of diplamine. [reaction: see text]

Regiochemistry in 1,3-dipolar cycloadditions of the azomethine ylide formed from diethyl aminomalonate and paraformaldehyde.

The azomethine ylide derived from the condensation of diethyl aminomalonate with paraformaldehyde undergoes 1,3-dipolar cycloadditions with acrylate and propiolate derivatives. Contrary to a previous report, these reactions yield mixtures of regioisomers generally favoring the 2,2,3-trisubstituted product. However, the relative quantity of the 2,2,4-trisubstituted product formed increases with an increase in the size of the activating group on the dipolaroplile.

A synthetic approach to the Stemona alkaloids.

This paper describes our work developing a strategy for the construction of the typical core structure of the Stemona alkaloids. The approach is to control the relative stereochemistry of the groups on the core 1-azabicyclo[5.3.

Synthesis of the C1-C28 Portion of Spongistatin 1 (Altohyrtin A).

A synthetic approach was developed to the C1-C28 subunit of spongistatin 1 (altohyrtin A, 65). The key step was the coupling of the AB and CD spiroketal moieties via an anti-aldol reaction of aldehyde 62 and ethyl ketone 57. The development of a method for the construction of the AB spiroketal fragment is described and included the desymmetrization of C(2)-symmetric diketone 10 and the differentiation of the two primary alcohols of 16.

Total Synthesis of (+/-)-Cylindricines A and B.

Cylindricine A (1) and cylindricine B (2) have been synthesized in 11 steps and 19% overall yield. The key reaction involves the addition of an organocopper species to a bicyclic vinylogous amide, which provides complete stereocontrol over the installation of the hexyl side chain.

Total Synthesis of Myxalamide A.

The polyene antibiotic myxalamide A (1) has been prepared by total synthesis. The synthesis illustrates a useful strategy for synthesis in which the high 1,2-stereocontrol achievable with the aldol reaction can be parlayed by other stereoselective processes so as to give compounds having two or more stereocenters with remote relationships. Application of the Evans asymmetric aldol reaction to aldehyde 13 gives the beta-hydroxy imide 17.

A Biomimetic Approach to the Discorhabdin Alkaloids: Total Syntheses of Discorhabdins C and E and Dethiadiscorhabdin D.

The characteristic spirodienone structure of the discorhabdin alkaloids is readily formed by reaction of the tyramine-substituted indoloquinonimines 26, 35, and 36 with cupric chloride, triethylamine, and oxygen. This cyclization provides a possibly biomimetic route to discorhabdins C and E (41 and 42). The unbrominated spirodienone 40 reacts with hydrogen over Pd/C to give enone 46.

Total Synthesis of Tricolorin A.

Tricolorin A (1) is a novel tetrasaccharide macrolactone that is a natural herbicide. In this paper is reported a total synthesis of 1. Coupling of hydroxy ester 18 with D-fucosyl trichloroacetimidate 23 gave fucoside 24.

Further studies of the Daphniphyllum alkaloid polycyclization cascade.

The scope of the 2-azadiene intramolecular Diels-Alder cyclization, previously employed for synthesis of the Daphniphyllum alkaloids, has been further investigated. Through a series of 1,5-diol cyclization precursors the substitution pattern of both the dienophile and the 2-azadiene were examined. From these studies it was shown that the cascade reaction is tolerant toward a variety of alkyl-substituted dienophiles.

alpha,beta-epoxy vinyl triflates in Pd-catalyzed reactions.

[reaction: see text] Reactions of steroidal alpha,beta-epoxy vinyl triflates in Pd-catalyzed reactions are described. Oxidative insertion of Pd(0) into the C-O bond, giving vinylpalladium 12, is faster than formation of the pi-allyl derivative from the vinyl epoxide. Although 12 can be trapped under certain conditions, it eventually rearranges to palladium alkoxide 14, which is in equilibrium with 15 and/or 10.

Synthesis of the C29-C44 portion of spongistatin 1 (altohyrtin A).

Two synthetic approaches to the C29-C44 portion of spongistatin 1 (altohyrtin A) have been developed. The key step of the first approach relies on the Claisen rearrangement of glucal 18 to provide ester 20a. This intermediate was advanced to silyl enol ether 30, which was coupled under Mukaiyama aldol conditions with aldehyde 3.

A method for constructing the C44-C51 side chain of altohyrtin C.

[formula: see text] A method to construct the C44-C51 side chain of altohyrtin C has been developed and applied to a model aldehyde derived from D-glucose. The approach relies on a Wittig reaction to couple the side chain to an aldehyde and utilizes an allylic diazene rearrangement to place the C45 double bond in the correct position.

Total synthesis of (+/-)-isoschizogamine.

[formula: see text] Isoschizogamine has been prepared for the first time. The synthesis requires eight steps from a readily available ketone starting material and features an aminal-forming cyclization that is based on a proposed biosynthetic transformation.

Total syntheses of (+/-)-preussomerins G and I.

[formula: see text] Preussomerins G and I (2 and 3) have been synthesized for the first time. The key reaction in the synthesis is a possibly biomimetic tautomerization reaction depicted in Scheme 3 and the foregoing graphic. The driving force for this interesting rearrangement is primarily derived from the increase in resonance energy associated with converting a naphthalene ring into two isolated benzene rings.

Synthesis of a model for C7-C13 of lankamycin.

[structure: see text] A convenient method is reported for construction of the C7-C13 segment of the macrolide antiobiotic lankamycin.

Total synthesis of (+/-)-aspidospermidine.

(+/-)-Aspidospermidine (1) has been synthesized from readily available methyl 3-ethyl-2-oxocylo-pentanecarboxylate (17) in 5.9% yield over 13 steps. The key step of the synthesis is an intramolecular cascade reaction that simultaneously forms the B, C, and D rings of 1.