Abstract:TheNMRmethodologybasedonspectralaliasingdevelopedattheUniversityofGenevaisreviewed. Differentapproachesaimedatincreasingtheresolutionintheindirectcarbondimensionof2Dheteronuclear experimentsarepresentedwiththeirrespectiveadvantages.ApplicationstoHSQC,HMBCandother2Dhet-eronuclearexperimentstothestudyofnaturalproductsandsynthesisintermediatesareshown.HSQC-based experimentsfordiffusionmeasurements,kineticsstudiesandtitrationsexperimentsalltakeadvantageofspectralaliasingtoreducetheexperimentaltimefromunrealisticallylongacquisitiontimestoovernightexperiments. TherolesofcomputationalmethodssuchasDFT/GIAOandLogicforStructureDetermination(LSD)instructure determinationarediscussed.

The methodology should find many applications in dimeric and oligomeric compounds such as peptides, carbohydrates, polyketides and other cases where signal clustering is expected.

The study of the MeOH extract of the leaves of Campylospermum excavatum led to the isolation of a nitrile glucoside, named campyloside C (1) and an original derivative of ochnaflavone, 7-O-methylochnaflavone (2), along with three known biflavonoids, amentoflavone, sequoiaflavone, and sotetsuflavone (3 - 5). The linkage site of the sub-units of 2 was confirmed by chemical correlation, after semi-synthesis of a trimethoxylated derivative of ochnaflavone (2a). The structures of these compounds as well as their relative and absolute configurations were assigned by 1D- and 2D-NMR experiments, HR-ESI-MS and Electronic Circular Dichroism (ECD) calculations. A low-pass J filter HMBC experiment was performed in order to define the configuration of the double bond of 1. All of the biflavonoids were evaluated against protozoan parasites. Amentoflavone moderately inhibited the promastigote form of Leishmania infantum.

Two new flavone glycosides, 3″-O-acetyl-7-O-methylvitexin (1) and 6″-α-rhamnopyranosyl-7-O-methylvitexin (2), along with nine known compounds (3-11) were isolated from the leaves of Rhabdophyllum arnoldianum (Ochnaceae). The structures of the new compounds were established by detailed spectroscopic studies and mass spectrometry, while known compounds were characterised by direct comparison of their reported NMR data with those found in the literature. All these compounds were the first reported from Rhabdophyllum genus. The biological assays on crude extracts and compounds of this plant demonstrated that the crude extracts possess significant antimicrobial activity against Gram-positive bacteria.

A new indole alkaloid, calanthumindole (4), and three known biflavonoids, amentoflavone, sequoiaflavone, and podoscarpusflavone B, were isolated from Campylospermum calanthum (Ochnaceae). Calanthumindole is a new indole alkaloid of the serotobenine family characterized by the presence of a CC bond between atoms C(7′) and C(8′) of the furan ring. This is the first compound to have a fully unsaturated furan ring among the members of this family. The combination of NMR and DFT allowed the determination and comparison of the 3D structures and relevant conformational characteristics of serotobenine (1), flavumindole (2), and calanthumindole (4).

Alkylglycerols (AKGs) with a straight-chain alkane or alkene are ether lipids abundant in the liver oil of some elasmobranch fish species such as ratfishes and some sharks. Natural shark liver oil (SLO) mixture displays several known biological activities and most of its identified alkylglycerols were also obtained individually in pure form by total synthesis. However, the synthesis of alkylglycerols containing at least one alkyne moiety in the alkyl chain has yet not been reported. In this work, we describe the first total synthesis of 1-O-alkylglycerols based alkyne (2S)-3-((4-methoxytridec-6-yn-1-yl)oxy)propane-1,2-diol ( 10) and (S)-3-(((R)-12-methoxyoctadec-9-yn-1-yl)oxy)propane-1,2-diol (11), analogues of bioactive ether lipids found in the SLO mixture. Oxiranes opening by alkynyl boranes and solketal etherification are the key steps with a global yield up to 72 % in eight steps sequence.

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