Study of alkaloids of the Siberian and Altai flora. 7. Synthesis of 18-amino-18-deoxy derivatives of elatidine

Reduction of elatidal oxime and imines based on methylamine, ethanolamine, tyramine, and S- and (±)-alaninols gave rise to the 18-amino-18-deoxy derivatives of elatidine.     

Using Natural Cinchona Alkaloids to Promote the Enantioselective Addition of Dialkylzinc to N－Diphenylphosphinylimines

Cinchona alkaloids are utilized as chiral ligands to promote the enantioselective addition of dialkylzinc to N-diphenyiphosphinylirnlnes affording enantiomerically enriched N-diphenyiphosphinylamines in up to 91% ee.     

Daminin, a bioactive pyrrole alkaloid from the Mediterranean sponge Axinella damicornis

The isolation and characterization of the known pyrrole alkaloid agelongine (6) and of the new natural product daminin (7), the bromine-free analogue of 6, from a specimen of the marine sponge Axinella damicornis is described. Compound 7 showed significant neuroprotective properties. Moreover, for the supply of sufficient material for future medicinal investigations, a short total synthesis of 7 was developed.     

Chemical Constituents from the Fermented Mycelia of the Medicinal Fungus Xylaria nigripes

Nineteen compounds mainly including pyrrole‐containing alkaloids and phytosterols were isolated from the EtOH extract of the fermented mycelia of Xylaria nigripes, a precious medicinal fungus known as Wuling Shen in Chinese. On the basis of spectroscopic methods, the structures of the new naturally occurring compounds were determined to be (4S)‐3,4‐dihydro‐4‐(4‐hydroxybenzyl)‐3‐oxo‐1H‐pyrrolo[2,1‐c][1,4]oxazine‐6‐carbaldehyde ( 1 ), methyl (2S)‐2‐[2‐formyl‐5‐(hydroxymethyl)‐1H‐pyrrol‐1‐yl]‐3‐(4‐hydroxyphenyl)propanoate ( 2 ), and 3‐{4‐[(2R)‐(2,3‐dihydroxy‐3‐methylbutoxy]phenyl}‐7‐hydroxy‐4H‐chromen‐4‐one ( 3 ), respectively. The absolute configurations of 1 and 2 were deduced by the observed Cotton effects in their circular dichroism (CD) spectra, whereas that of the 1,2‐diol moiety in 3 was determined using the Snatzke's method. Their biological activities such as neuroprotective, anti‐neuroinflammatory, and cytotoxic properties were also reported.     

Three new pyrrolizidine alkaloids derivatives from Liparis nervosa

Three new pyrrolizidine alkaloids, nervosine VⅡ (1), nervosine VⅢ(2) and nervosine Ⅸ(3) were isolated from the whole plant extract of Liparis nervosa. Their structures were elucidated by extensive spectroscopic analyses(including 1D, 2D NMR, and HR-ESI-MS) and chemical methods. Compounds 1–3were evaluated for their cytotoxic activity against A549, MCF-7and H460 human cancer cell lines.     

Napelline-type C_(20)-diterpenoid alkaloid iminiums from an aqueous extract of ‘‘fu zi': Solvent-/base-/acid-dependent transformation and equilibration between alcohol iminium and aza acetal forms

Three new napelline-type C₂₀-diterpenoid alkaloids, named aconicarmichinium A and B trifluoroacetates (1 and 2) and aconicarmichinium C chloride (3), were isolated from an aqueous extract of “fu zi”, the lateral roots of Aconitum carmichaelii. Their structures were elucidated by extensive spectroscopic data analysis. Compounds 1-3 represent the first examples of napelline-type C₂₀-diterpenoid alkaloid alcohol iminiums, of which the structures were fully characterized. In addition, transformation and equilibration between the alcohol iminiums (1-3) and the aza acetals 1a-3a were investigated by measurements of the NMR spectra in protic and aprotic deuteriumsolvents including alkali pyridine-d₅, along with evaporation under reduced pressure and gradual additions of TFA, AcOH, and HCl. The results demonstrated that the transformation and equilibration were solvent-, base-, and acid-dependent. Especially, in aqueous biological fluid, these C₂₀-diterpenoid alkaloids would more likely exist as the alcohol iminiums accompanied by anion counterparts in biosystems to increase their solubility, bioavailability, transportations, and functions. The absolute configurations of 1-3 were confirmed by X-ray crystallographic analysis of 2a.     

Studies on the Enantioselective Synthesis of E-Ethylidene-bearing Spiro[indolizidine-1,3′-oxindole] Alkaloids

A synthetic route for the enantioselective construction of the tetracyclic spiro[indolizidine-1,3′-oxindole] framework present in a large number of oxindole alkaloids, with a cis H-3/H-15 stereochemistry, a functionalized two-carbon substituent at C-15, and an E-ethylidene substituent at C-20, is reported. The key steps of the synthesis are the generation of the tetracyclic spirooxindole ring system by stereoselective spirocyclization from a tryptophanol-derived oxazolopiperidone lactam, the removal of the hydroxymethyl group, and the stereoselective introduction of the E-ethylidene substituent by acetylation at the α-position of the lactam carbonyl, followed by hydride reduction and elimination. Following this route, the 21-oxo derivative of the enantiomer of the alkaloid 7(S)-geissoschizol oxindole has been prepared.     

Scopuquinolone B,a new monoterpenoid dihydroquinolin-2(1H)-one isolated from the coral-derived Scopulariopsis sp. fungus

Further chemical investigation of the secondary metabolites of the fungus Scopulariopsis sp. led to the discovery of a new alkaloid, scopuquinolone B (1). The structure of compound 1 was elucidated by extensive NMR spectroscopic data, CD spectrum and analysis of its Dess-Martin oxidation derivative. Compound 1 was evaluated for antilarval settlement activity of barnacle Balanus amphitrite and showed promising antifouling activity with an EC₅₀ value of 0.103 μM and a high therapeutic ratio of 222.