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[EN] The feasibility of an electron transfer imino-Diels Alder reaction betweenN-benzylideneaniline and arylalkenes in the presence of a pyrylium salt as a photosensitizer has been demonstrated by a combination of product studies, laser flash photolysis (LFP), and DFT theoretical calculations. A stepwise mechanism involving two intermediates and two transition states is proposed., Financial support from the MICINN (Grants CTQ2010-14882, CTQ2009-13699, CTQ2009-11027, and JCI-2010-06204) and from the UPV (Grant No. 20100994 and MCI Program) is gratefully acknowledged. Dedicated to Prof. Dr. Jaime Primo (Universidad Politecnica de Valencia) on the occasion of his 60th birthday.

The martinelline chiral core 3 and its diastereomer were synthesized by using the asymmetric tandem Michael–aldol reaction as the key step from 4-methoxycarbonylanthranilaldehyde and the α,β-unsaturated aldehyde.

The simple and one-pot method for the synthesis of polysubstituted tetrahydroquinolines from readily available anilines and aldehydes under reagent-free conditions has been developed. The scope of the transformation has been demonstrated. This method has been successfully applied to the rapid formal synthesis of (±)-martinellic acid and martinelline.

Formal [4+2] cycloaddition of cyclic enamides with imines derived from aromatic amines gave the 4-arylhexahydropyrroloquinoline skeleton in one step as mixtures of diastereoisomers. Aromatic imines derived from formaldehyde and methylglyoxalate also participated in this chemistry, with the latter favouring formation of the endo -cycloadduct. The cycloadducts derived from methylglyoxalate were unstable and fragmented to give highly substituted quinolines under both neutral and basic conditions. Imines derived from 3-cyanoacrolein also underwent cycloaddition and gave an advanced potential precursor to martinellic acid, albeit with poor diastereoselectivity.

Hindered guanidines can be prepared by reaction of cyanamides with amines in hexafluoroisopropanol at 90–120°C. This sequence was used for preparing guanidinium acid 21 as a model for martinellic acid.

The tricyclic core of the martinellines has been synthesised stereoselectively in two steps, using 1,3-dipolar cycloaddition of azomethine ylides as a key step.

The tricyclic triamine core27 of martinellic acid (2) has been prepared stereospecifically in eight steps from 2-hydroxymethylaniline in 11% overall yield. The key steps are the addition of 2-hydroxymethylaniline to vinylcyclopropane14 to prepare cycloaddition precursor19 in only two steps and an intramolecular [3+2] azomethine ylide cycloaddition reaction to produce tetracycle20 with>9:1 diastereoselectivity. Download : Download full-size image

An expedient method for the assembly of the pyrroloquinoline skeleton found in the martinelline alkaloids using a [3+2] cycloaddition of an azomethine ylide and an alkene has been developed.

Radical cyclisation of the N-(2′-iodophenyl)pyrrole-3-carboxamides 5 and 6 gave the tricyclic pyrrolo [3,2-c]quinolone ring system found in the recently isolated martinelline 1 and martinellic acid 2.

[reaction: see text] The first total synthesis of martinellic acid, a naturally occurring bradykinin receptor antagonist, via a CuI-catalyzed coupling reaction of beta-amino ester 6 with 1,4-diiodobenzene and a guanylation reaction of secondary amine 3 under mild conditions as key steps, is described.

Arylthio-substituted succinic anhydrides undergo cycloaddition reactions with imines to produce gamma-lactams in high yield and with high diastereoselectivity. The origin of the selectivity is proposed to result from anion-pi repulsion in the transition state. The utility of this technique is demonstrated in a synthesis of the carbon framework common to the alkaloids martinellic acid and martinelline in five steps.

A concise formal total synthesis of the pyrrolo[3,2-c]quinoline containing natural product, martinellic acid, has been achieved from a pyrroloquinol-2-one through addition of a copper acetylide to an iminium ion. Global deprotection and alkyne reduction then provides the tricyclic triamine, which can be converted to martinelline and martinellic acid.

[reaction: see text] A concise synthesis of the guanidine alkaloids, (+/-)-martinelline and (+/-)-martinellic acid, using a protic acid catalyzed 2:1 hetero Diels-Alder coupling reaction between N-Cbz 2-pyrroline and methyl 4-aminobenzoate, is described. Protic acid catalysis, rather than Lewis acid catalysis, was necessary to achieve the desired sense of diastereocontrol in the coupling reaction.

Background Candida susceptibility commonly occurs in breast cancer patients. Of which, Candida albicans is considered as a common pathogen causing candidiasis. Martinella iquitosensis (Bignoniaceae) is one of the species belonged to Martinella, distributed widely in Amazon basin. Its root extract yielded two complex substituted tetrahydroquinolines, Martinelline and Martinellic acid which were the first natural non-peptide bradykinin receptor antagonists identified. Findings In this study, a novel martinelline type analogue, named 2,3,3a,4,5,9b-hexahydro-8-phenoxy-4-(pyridin-2-yl)furo[3,2-c]quinoline, was synthesized and its preliminary anticancer activity and antifungal potential were investigated. This compound showed potential anticancer activity against MDAMB-231 breast cancer cells. Meanwhile it could enhance the fungistatic activity of miconazole against Candida albicans. Conclusions These findings provide an implication for the continue investigation and development of martinelline type analogues as therapeutic agents in the future.