Concise asymmetric syntheses of (+)- and (−)-tetraponerine-8, (+)- and (−)-tetraponerine-7, and their ethyl homologues. A correction of the structures of tetraponerine-3, and -7

Synthesis of pyrimidine-containing alkaloids

This review deals with the synthesis of naturally occurring alkaloids containing partially or completely saturated pyrimidine nuclei. The interest in these compounds is associated with their structural diversity, high biological activity and toxicity. The review is divided into four parts, each of which describes a number of synthetic methodologies toward structurally different naturally occurring alkaloids containing saturated cyclic six-membered amidine, guanidine, aminal and urea (thiourea) moieties, respectively. The development of various synthetic strategies for the preparation of these compounds has remarkably increased during the past few decades. This is primarily due to the fact that some of these compounds are isolated only in limited quantities, which makes it practically impossible to study their full structural characteristics and biological activity.

Stereocontrolled synthesis of bicyclic ureas and sulfamides via Pd-catalyzed alkene carboamination reactions

The synthesis of bicyclic ureas and sulfamides via palladium-catalyzed alkene carboamination reactions between aryl/alkenyl halides/triflates and alkenes bearing pendant cyclic sulfamides and ureas is described. The substrates for these reactions are generated in 3-5 steps from commercially available materials, and products are obtained in good yield with up to >20:1 diastereoselectivity. The stereochemical outcome of the sulfamide alkene addition is consistent with a mechanism involving anti-aminopalladation of the alkene, whereas the stereochemical outcome of the urea alkene addition is consistent with a syn-aminopalladation mechanism.

Natural tetraponerines: a general synthesis and antiproliferative activity

A stereocontrolled general methodology to access all natural tetraponerines from (+)-T1 to (+)-T8 is detailed. Two consecutive indium-mediated aminoallylations with the appropriate enantiomer of chiral N-tert-butylsulfinamide and a thermodynamic control at the aminal stereocenter allow the formation of each natural tetraponerine with excellent stereoselectivity. The use of 4-bromobutanal in the first aminoallylation leads to the formation of 5-6-5 tetraponerines, while 5-bromopentanal is required to build the scaffold of 6-6-5 tetraponerines. A cross-metathesis reaction of the second aminoallylation product with cis-3-hexene is used to elongate the side chain up to 5 carbons so as to prepare the tetraponerines T5 to T8. The anticancer activity of these heavier tetraponerines against four different carcinoma human cell lines is examined, observing a promising cytotoxic activity of (+)-T7 against breast carcinoma cell line MCF-7.

Concise total synthesis and stereochemical analysis of tetraponerines T3 and T4

An efficient stereocontrolled preparation of tetraponerines T3 and T4 is detailed. The sequence takes advantage of two consecutive stereoselective aminoallylations of appropriate aldehydes with chiral tert-butanesulfinamide and in situ generated allyl indium species. The absolute configuration of the carbon stereogenic center at the aminal moiety is thermodynamically controlled. This was ascertained on the basis of an exhaustive DFT configurational study of tetraponerines, which fulfils the lack of detailed structural information for these systems. It was found that the trans-transoid-configuration of the AB rings is the most stable geometry for T3 and T4. However, the C ring prefers a cis-configuration in T3 (ttc-T3) and a trans-fusion in T4 (ttt-T4). Regarding their dynamic behavior, low activation barriers were found by DFT calculations for the inversion of the nitrogen at the indolizidine framework, allowing rapid equilibration between the major configurations (ttc and ttt) in T3 and T4.

N-[(Z)-4-Methoxybenzylidene](methoxycarbonyl)methanamine oxide

The title compound, C₁₁H₁₃NO₄, contains a nitrone group, C=N—O—R, the geometry of which shows a Z configuration with near planarity (r.m.s. deviation = 0.0787 Å) around the C=N double bond. An intra­molecular C—H⋯O hydrogen bond generates an S(6) ring motif. In the crystal packing, mol­ecules are linked into R₂²(12) dimers and R₂²(14) rings via C—H⋯O inter­molecular hydrogen bonds.

Electrophilic Activation of Lactams with Tf2O and Pyridine: Expedient Synthesis of (±)-Tetraponerine T4

[reaction: see text] The electrophilic activation of lactams with triflic anhydride in the presence of pyridine was investigated by NMR. It was found that 2-pyrrolidone led to the clean formation of the corresponding pyridinium imidate in 89% isolated yield. The subsequent nucleophilic addition of organometallic reagents led to 2-substituted dihydropyridines. A synthesis of (+/-)-tetraponerine T4 with three simple building blocks was accomplished in 3 steps (38% yield).

Highly Stereoselective Synthesis of Functionalized β,β-Di- and Trisubstituted Vinylic Sulfoxides by Cu-Catalyzed Conjugate Addition of Organozinc Reagents

beta,beta-Disubstituted chiral vinylic sulfoxides bearing functionalities have been synthesized via Cu-catalyzed conjugate addition of organozinc reagents to chiral 1-alkynyl sulfoxides. Due to the availability of functionalized organozinc reagents and high syn-selectivity of the reaction, both geometric beta,beta-disubstituted vinylic sulfoxides were selectively synthesized. Furthermore, 1-alkynyl sulfoxides were derivatized into trisubstituted vinylic sulfoxides by trapping the resulting alpha-sulfinyl vinylic carbanion with electrophiles. Highly diastereoselective THF and THP ring formations were accomplished by means of this methodology followed by an intramolecular Michael addition.

Ammonia chemical ionization tandem mass spectrometry in structural determination of alkaloids. II. Tetraponerines from pseudomyrmecine ants

Chemical ionization tandem mass spectrometry (CI-MS/MS) of alkaloids with ammonia reagent gas and collision-activated dissociation as well as EI-MS/MS were applied to the tetraponerine alkaloids in extracts from six pseudomyrmecine ants of the genus Tetraponera. The MS/MS techniques along with gas chromatography Fourier transform infrared (GC/FTIR) spectra allowed identification in two extracts of seven of the eight known tetraponerines. The EI-MS/MS fragmentations proved diagnostic for the ring system and the CI-MS/MS patterns for the C-8 or C-9 substitution, while the Bohlmann bands in FTIR spectra were diagnostic for the C-8 or C-9 configurations. An Indian ant (T. allaborans) had T-2, T-4 and T-8, while a Chinese ant (T. binghami) had T-5, T-6, T-7 and T-8. Four other ants, T. rufonigra (India), T. penzigi (Africa), T. clypeata (Africa) and T. sp. cf. emeryi (Africa), had no tetraponerines.