Total synthesis of (-)-uniflorine A

Total synthesis of (-)-uniflorine A (3) has been accomplished in nine steps and 11% overall yield from carbohydrate-based nitrone 5. The key steps of the synthetic strategy were a high regio- and complete stereoselective 1,3-dipolar cycloaddition of alkene 6 with nitrone 5, a Tamao-Fleming reaction for replacing the silicon substituent with a hydroxy group with retention of configuration, and a Mitsunobu reaction to establish the correct configuration of the target molecule at C-6.

Diastereoselective pyrrolidine synthesis via copper promoted intramolecular aminooxygenation of alkenes: formal synthesis of (+)-monomorine

The diastereoselectivity of the copper-promoted intramolecular aminooxygenation of various alkene substrates was investigated. Alpha-substituted 4-pentenyl sulfonamides favor the formation of 2,5-cis-pyrrolidines (dr >20:1) giving excellent yields which range from 76-97% while gamma-substituted substrates favor the 2,3-trans pyrrolidine adducts with moderate selectivity (ca. 3:1). A substrate whose N-substituent was directly tethered to the alpha-carbon exclusively yielded the 2,5-trans pyrrolidine. The synthetic utility of the method was demonstrated by a short and efficient formal synthesis of (+)-monomorine.

Total synthesis of the lycopodium alkaloid (+)-serratezomine A

The first total synthesis of (+)-serratezomine A is described. Key aspects of the synthesis include (a) the first deployment of free-radical-mediated vinyl amination (an intramolecular alkyne aminostannation) in a complex target synthesis, (b) the use of a beta-stannyl enamine as the lynchpin for convergent assembly of the natural product backbone, (c) the use of an oxidative allylation promoted by cerium(IV) (CAN) to establish the all-carbon quaternary chiral center with the proper configuration, and (d) an intramolecular substitution reaction to form the sensitive bridging lactone. Overall, 15 steps (longest linear sequence) are required to prepare the natural product from a commercially available aldehyde, and assembly of the contiguous array of six stereocenters is accomplished with high stereocontrol.

Natural products as inspiration for the development of asymmetric catalysis

Biologically active natural products often contain particularly challenging structural features and functionalities in terms of synthesis. Perhaps the greatest difficulties are those caused by issues of stereochemistry. A useful strategy for synthesizing such molecules is to devise methods of bond formation that provide opportunities for using enantioselective catalysis. In using this tactic, the desire for a particular target structure ultimately drives the development of catalytic methods. New enantioselective catalytic methods contribute to a greater fundamental understanding of how bonds can be constructed and lead to valuable synthetic technologies that are useful for a variety of applications.

Synthesis and evaluation of heteroaromatic 6,7-diaryl-2,3,8,8a-tetrahydroindolizin-5(1H)-ones for cytotoxicity against the HCT-116 colon cancer cell line

A heteroaromatic 6,7-diaryl-2,3,8,8a-tetrahydroindolizin-5(1H)-one analog library was prepared and tested for cytotoxic properties against the HCT-116 colon cancer cell line, thus providing additional information pertaining to structure-activity relationships for this class of compounds. The most active of the new analogs proved to be the C6 2-thiophene and 3-thiophene analogs with IC(50) values of 0.27 microM and 0.60 microM, respectively.

Efficient Synthesis of a New Structural Phenanthro[9,10,3‘,4‘]indolizidine Starting from Pyrrole

A new structural phenanthroindolizidine, 2,3,6,7-tetramethoxyphenanthro[9,10,3',4']indolizidine, has been synthesized efficiently from pyrrole. An important feature of this synthesis is that intramolecular oxidative coupling and rearrangement of 6,7-bis(3,4-dimethoxyphenyl)-8-methoxy-1,2,3-trihydroindolizin-5-one by using VOF3 and TFA have been achieved in one pot.

Thiophenol-Mediated 1,5-Hydrogen Transfer for the Preparation of Pyrrolizidines, Indolizidines, and Related Compounds

The efficient preparation of 1-azabicyclic alkanes is described. Highly functionalized skeletons are prepared in a concise manner using a radical tin-free 1,5-hydrogen transfer-cyclization process. The precursors for the radical reactions are readily assembled either from pyrrolidine/piperidine/hexahydro-1H-azepine or via condensation of a properly designed N-alkylimine with an allenylzinc species.

Total synthesis of pumiliotoxins 209F and 251D via late-stage, nickel-catalyzed epoxide-alkyne reductive cyclization

Pumiliotoxins 209F and 251D were synthesized using highly selective nickel-catalyzed epoxide-alkyne reductive cyclizations as the final step. The exocyclic (Z)-alkene found in the majority of the pumiliotoxins was formed stereospecifically and regioselectively, without the use of a directing group on the alkyne, and the epoxide underwent ring opening exclusively at the less hindered carbon to provide the requisite tertiary alcohol. The epoxides were prepared using diastereoselective addition of a sulfoxonium anion to a proline-derived methyl ketone.

Gold-Catalyzed Multicomponent Synthesis of Aminoindolizines from Aldehydes, Amines, and Alkynes under Solvent-Free Conditions or in Water

A gold(III)-catalyzed multicomponent coupling/cycloisomerization reaction of heteroaryl aldehydes, amines, and alkynes under solvent-free conditions or in water has been developed. This methodology provides rapid access to substituted aminoindolizines with high atom economy and high catalytic efficiency. Especially, the coupling of enantiomerically enriched amino acid derivatives produces the corresponding N-indolizine-incorporated amino acid derivatives without loss of enantiomeric purity.

Highly Efficient Synthesis of Functionalized Indolizines and Indolizinones by Copper-Catalyzed Cycloisomerizations of Propargylic Pyridines

The copper-catalyzed cycloisomerizations of 2-pyridyl-substituted propargylic acetates and its derivatives are described, which offer an efficient route to C-1 oxygenated indolizines with a wide range of substituents under mild reaction conditions. The presented method could be readily applied to the synthesis of indolizinones through a cyclization/1,2-migration of tertiary propargylic alcohols.

Short and efficient total synthesis of luotonin A and 22-hydroxyacuminatine using a common cascade strategy

Total syntheses of 22-hydroxyacuminatine and luotonin A were achieved in direct fashion and high overall yields (16% in eight steps and 47% in five steps, respectively). A mild cascade methodology was successfully applied in both syntheses as a common strategy. The new approach presents the advantages of short routes, high overall yields, use of stable intermediates, and ease of operations.

Antitumor agents 253. Design, synthesis, and antitumor evaluation of novel 9-substituted phenanthrene-based tylophorine derivatives as potential anticancer agents

C9-Substituted phenanthrene-based tylophorine derivatives (PBTs) (13-36) were synthesized and evaluated as in vitro anticancer agents against the human A549 lung cancer cell line. Twelve active compounds were further examined against DU-145 (prostate), ZR-751 (breast), KB (nasopharyngeal), and KB-Vin (multidrug resistant KB subline) human cancer cell lines. They showed potent cytotoxic activity against both wild type and matched multidrug resistant KB cell lines, and displayed notable selectivity toward DU-145 (prostate) and ZR-751 (breast) cancer cell lines. The mode of action of this class may be distinctly different from that of other cancer chemotherapeutic compounds. Three PBT analogs were also evaluated in a murine model. Compound 24b showed modest in vivo antitumor activity against human A549 xenograft in nude mice as well as potent in vitro cytotoxic activity, and thus, is a promising anticancer lead compound.

Asymmetric synthesis of (-)-nupharamine and (-)-(5S,8R,9S)-5-(3-furyl)-8-methyloctahydroindolizidine from beta-amino ketones and the intramolecular Mannich reaction

The asymmetric synthesis of the 2,3,6-trisubstituted piperidine core of the antitumor Nuphar alkaloids was readily achieved by using the intramolecular Mannich reaction and a sulfinimine-derived beta-amino ketone.

Total syntheses of the tylophora alkaloids cryptopleurine, (-)-antofine, (-)-tylophorine, and (-)-ficuseptine C

A concise, efficient and modular approach to the tylophora alkaloids is described, a family of potent cytotoxic agents that are equally effective against drug sensitive and multidrug resistant cancer cell lines. The advantages of the chosen route are illustrated by the total syntheses of the phenanthroquinolizidine cryptopleurine (1) and the phenanthroindolizidines (-)-antofine (2), (-)-tylophorine (3), and their only recently isolated congener (-)-ficuseptine C (4). The key steps consist in a Suzuki cross-coupling between a (commercial) boronic acid and a simple aryl-1,2-dihalide followed by elaboration of the resulting products into the corresponding 2-alkynyl-biphenyl derivatives 27, 33, 41 and 46. The latter undergo PtCl2-catalyzed cycloisomerizations with formation of the functionalized phenanthrenes 28, 34, 42 and 47, which were transformed into the targeted alkaloids by a deprotection/Pictet-Spengler annulation tandem. Due to the flexibility and robust character of this approach, it might enable a systematic exploration of the pharmacological profile of this promising class of bioactive natural products.

General Strategy for the Construction of Enantiopure Pyrrolidine-Based Alkaloids. Total Synthesis of (−)-Monomorine

An enantiopure cis-2,5-disubstituted pyrrolidine building block was prepared from cocaine. The synthetic utility of this compound as a chiral building block was demonstrated by a short and efficient synthesis of the pyrrolidine-based alkaloid (-)-monomorine (six steps, 37% overall yield).

Pt-catalyzed cyclization/1,2-migration for the synthesis of indolizines, pyrrolones, and indolizinones

Indolizine, pyrrolone, and indolizinone heterocycles are easily accessed via the Pt(II)-catalyzed cycloisomerization or a tandem cyclization/1,2-migration of pyridine propargylic alcohols and derivatives. This method provides an efficient synthesis of highly functionalized heterocycles from readily available substrates. [reaction: see text]

Synthesis andIn Vitro Cytotoxicity Evaluation of Novel Naphthindolizinedione Derivatives

Novel 6,11-dioxo-6,11-dihydro-benzo[f]pyrido[1,2-a]indole-12-carboxamide derivatives and the corresponding 7,10-dihydroxy analogues were designed in accordance with Moore's and Pindur's theory and synthesized based on the structural similarity with known antitumour agents such as ellipticine, daunorubicin, mitoxantrone and 9-aminoacridine-4 carboxamide derivatives. These compounds, including structural variations of the amide side chain, were evaluated in the NCI panel of human tumour cell lines, from which 6,11-dioxo-6,11-dihydro-benzo[f]pyrido[1,2-a]indole-(2-dimethylamino-ethyl)-12-carboxamide 11a was found to be the most potent agent within the series. It showed good selectivity towards leukaemia, colon and renal cancer cell lines, with significant GI50 values, from lower than 10 nM to 0.2 microM. Moreover, its cytotoxicity against the adriamicine-resistant breast tumour cell line at a concentration lower than 1 microM turned out to be higher than the values using the clinical anticancer agents, daunorubicin and mitoxantrone.

A Versatile Strategy for Divergent and Diastereoselective Synthesis of Natural Product-Like Polyhydroxylated Indolizidines

A general and versatile method for the divergent and diastereoselective synthesis of polyhydroxylated indolizidines has been established. The annulation reactions of a readily available enantiopure dihydroxylated cyclic secondary enamine with alpha,beta-unsaturated carboxylates including methyl acrylate, methyl crotonate, methyl 2-hexenoate, allenoate, and dimethyl acetylenedicarboxylate and with malonyl chloride produced hexahydro- or tetrahydro-5-indolizinone-8-carboxylates in high yields. The resulting 5-indolizinone derivatives were converted into diverse polyhydroxylated indolizidines in good yields through practical hydrogenation and reduction reactions.

Intramolecular azide trapping of the Nazarov intermediate: formation of peroxy-bridged indolizidinones via a deep-seated rearrangement and aerobic oxidation

Cross-conjugated dienones with pendent azide side chains undergo interrupted Nazarov trapping, leading to peroxy-bridged indolizidinones in good yields. This process is proposed to involve skeletal rearrangement of the initial trapping product, with loss of dinitrogen, to give an intermediate 1,4-betaine, which then undergoes reaction with atmospheric oxygen. The endoperoxide products can be reduced under catalytic hydrogenation conditions to furnish alpha-hydroxylactams. [reaction: see text].

Preparation of new nitrogen-bridged heterocycles. 59. Syntheses and intramolecular interactions of 3-(acylmethylthio)- and 3-[(3-ethoxycarbonyl-2-propenyl)thio]thieno[3,4-b]indolizine derivatives

Various thieno[3,4-b]indolizine derivatives having an acylmethylthio or (3-ethoxycarbonyl-2-propenyl)thio group at the 3-position which could not be obtained by a conventional method were prepared by a new procedure using cyanoethyl group as a protecting group and their intramolecular arene-pi interactions were investigated. In the (1)H-NMR spectra of these thieno[3,4-b]indolizines, the low-field shifts (delta 0.10-0.33 ppm) for the 5-protons were observed in comparison with those of 3-(methylthio)thieno[3,4-b]indolizines as a standard. The UV spectra also exhibited a characteristic absorption band at 425-445 nm attributable to the arene-pi interaction but their intensities were generally lower than those of 3-(arylmethylthio)thieno[3,4-b]indolizines. In their X-ray analyses, the anti conformation for 3-(acylmethylthio)thieno[3,4-b]indolizines and the gauche one for the 3-(3-ethoxycarbonyl-2-propenyl)thio derivatives were exhibited.

Synthesis of indolizine derivatives with selective antibacterial activity against Mycobacterium tuberculosis

1-substituted indolizines with activity against Mycobacterium tuberculosis have been synthesized. The most active compounds carry an hydroxyphenylmethyl- or hydroxyalkyl substituent in the indolizine 1-position. The alkyl chain should be moderately long (C-5 or C-6). Aryl groups in the 2- and 3-position of the indolizine are also required. Removal of the 3-substituent resulted in significant loss of activity. A nitrile substituent in the 7-position is beneficial for both chemical stability and bioactivity. The compounds studied display a narrow antibacterial spectrum and appear to be quite selective antimycobacterial compounds. Moderate activity against certain pathogenic protozoa was also observed.

Synthesis of (±)-Strychnofoline via a Highly Convergent Selective Annulation Reaction

Studies aimed at preparing (+/-)-strychnofoline by total synthesis are detailed. The route described makes use of a recently developed MgI(2)-mediated ring-expansion reaction of spiro[cyclopropan-1,3'-oxindole] with a cyclic disubstituted aldimine. The ring-expansion product was formed as a single diastereoisomer in 55 % yield, possessing the same stereochemical pattern found in strychnofoline. In addition, our synthetic effort has led to the development of new reaction methodology to access 3,4-disubstituted cyclic aldimines.