A new erythrinan N-oxide alkaloid from Erythrina stricta

This phytochemical study of stems and leaves of Erythrina stricta led to the isolation of twenty-three alkaloids, one of them previously unreported, 11β-hydroxyerythratidine N-oxide. Their structures were elucidated on the basis of extensive 1D and 2D NMR spectroscopic analyses including HSQC, HMBC, ¹H–¹H COSY, NOESY, as well as HRESIMS data in addition to comparison with reports in the literature.     

Fused N-Heterocycles with Contiguous Stereogenic Centers Accessed by an Asymmetric Catalytic Cascade Reaction of Tertiary Enamides

We report in this article a cascade reaction strategy for the synthesis of complex N-heterocyclic compounds with contiguous and tetrasubstituted stereogenic carbons. Under the sequential catalysis of a chiral binol–Ti complex and BF₃, cyclopentanone-derived tertiary enamides undergo an enantioselective enamine addition to ketone carbonyls followed by diastereoselective trapping of the resulting acyliminiums by electron-rich aryl moieties to furnish four- and five-membered ring-fused N-heterocyclic products as the sole diastereomers in high yields with up to 99 % ee.     

Transition-Metal-Free Multiple Functionalization of Piperidines to 4-Substituted and 3,4-Disubstituted 2-Piperidinones

Remote and multiple functionalization of piperidines without the use of transition-metal catalysts and elaborate directing groups is one of the major challenges in organic synthesis. Herein is reported an unprecedented two-step protocol that enables the multiple functionalization of piperidines to either 4-substituted or trans-3,4-disubstituted 2-piperidones. First, by exploiting the duality of TEMPO reactivity, which under oxidative and thermal conditions fluctuates between cationic and persistent-radical form, a novel multiple C(sp³)-H oxidation of piperidines to α,β-unsaturated 2-piperidones was developed. Second, the intrinsic low reactivity of the unsaturated piperidones toward conjugated Grignard additions was overcome by using trimethylsilyl chloride (TMSCl) as Lewis acid. Subsequently, conjugated Grignard addition/electrophilic trapping protocol provided substituted 2-piperidone intermediates, some of which were then transformed into pharmaceutical alkaloids.     

Asymmetric Organocatalysis: The Emerging Utility of α,β‐Unsaturated Acylammonium Salts

Although acylammonium salts are well‐studied, chiral α,β‐unsaturated acylammonium salts have received much less attention. While these intermediates are convenient synthons, which are readily available from several commodity unsaturated acids and acid chlorides, and possess three reactive sites, their application in organic synthesis has been limited because of the lack of appropriate chiral Lewis bases for their generation. In recent years, the utility of chiral, unsaturated acylammonium salts has expanded considerably, thus demonstrating the unique reactivity of this intermediate leading to the development of a diverse array of catalytic, asymmetric transformations including organocascade processes. This Minireview highlights the recent and growing interest in these intermediates which might spark further research into their untapped potential for asymmetric organocascade catalysis. A cursory comparison is made to related unsaturated iminium and acylazolium intermediates.     

Synthesis,Structure and Molecular Docking of New 4,5-Dihydrothiazole Derivatives Based on 3,5-Dimethylpyrazole and Cytisine and Salsoline Alkaloids

The interaction results of 1,2-dibromo-3-isothiocyanatopropane with some pyrazoles as well as cytisine and salsoline alkaloids were presented in this paper. It was shown that the reaction resulted in one one-step and rather mild method for the preparation of the corresponding 1,3-thiazoline bromomethyl derivatives. The yield of this reaction was affected by the presence of a base and an order in which reagents were added. Molecular docking of the synthesized 1,3-thiazoline derivatives for putative antibacterial activity was carried out using the penicillin-binding target protein (PBP4) of the bacteria E. coli “Homo sapiens” and S. aureus “Homo sapiens” as an example. Molecular docking demonstrated that the compounds had insignificant binding energies at the level of selected reference drugs (Cephalotin and Chloramphenicol). The presence of natural alkaloids in the structure of thiazoline derivatives somewhat increased the affinity of these substrates for target proteins selected.     

New Diterpenoid Alkaloids from Delphinium Souliei Franch

Inourpreviouspapers'-',wehavereportedtheisolationandelucidationofaseriesofnewditerpenoidalkaloidsfromDelphinillnlsolllieiFranch.ContinuedphytochemcalinvestigationsontheconstituentsofthisplanthaveledtotheisolationoftwoothernewditerpenoidalkaloidssoulineE(l)andsoulineF(2).SoulineE(2.6mg)wasobtainedascolorlesscrystals,mpf77-78'C(fromethanol).[a]."8.0(c=0.05,CHCI;).itsmolecularformulaC,=H;,NO,wasderivedfromHkEIMS(M-f361.2613,cafe.361.2608).TheiHnmrspectrum(400MHz)exhibitedthefollowingsign…     

Modification of Norditerpenoid Alkaloids:Ⅱ.A Simple andConvenient Preparation of the Imine Derivatives of Norditerpenoid Alkaloids

Interestthenloditlcationofthenorditerpenoidalkaloidsledustopreparationoftheiminederivatives.Preparationmethodsoftheimmeshavebeensummed.includingoxidationa"ithCrO,/pyridine=,rearrangementofchloroamines3andheatingsomeoxazolidine-containingorhavingO.N-mixednorditerpenoidalkaloidssuchasisoatisine1'andajaconine2',withAc=O-pyridine.Inaddition.oxidationof3'withPh(OAc).isalsousedtarthispurpose.In1995,Fuente,elalpreparedanimine5(21%)startingfromperegrine4byoxidationofKMnO./acetone-H,O(2;1)'.Inthe…     

Structural Basis and Enzymatic Mechanism of the Biosynthesis of C9‐ from C10‐Monoterpenoid Indole Alkaloids

Cutting carbons : The three‐dimensional structure of polyneuridine aldehyde esterase (PNAE) gives insight into the enzymatic mechanism of the biosynthesis of C₉‐ from C₁₀‐monoterpenoid indole alkaloids (see scheme). PNAE is a very substrate‐specific serine esterase. It harbors the catalytic triad S87‐D216‐H244, and is a new member of the α/β‐fold hydrolase superfamily. Its novel function leads to the diversification of alkaloid structures.