Université de Fribourg

Rauvolfianine, a new antimycobacterial glyceroglycolipid and other constituents from Rauvolfia caffra. Sond (Apocynaceae)

Messanga, Robert Ebeh ; Ngono Bikobo, Dominique Serge ; Zintchem, Auguste Abouem A. ; Mbabi Nyemeck, II Norbert ; Moni Ndedi, Esther Del Florence ; Betote Diboué, Patrick Hervé ; Nyegue, Maximilienne Ascension ; Atchadé, Alex De Théodore ; Pegnyemb, Dieudonné Emmanuel ; Bochet, Christian G. ; Koert, Ulrich

In: Natural Product Research, 2018, vol. 32, no. 16, p. 1971–1976

The chemical investigation of the extract of the dried leaves of Rauvolfia caffra (Sond) (synonym Rauvolfia macrophylla) (Apocynaceae) led to isolation of a new glycoside derivative, rauvolfianine (1) as well as six known compounds: oleanolic acid (2), sitosterol-3-O-β-D-glucopyranoside (3), betulinic acid (4), vellosimine (5), sarpagine (6) and...

Université de Fribourg

Application of photoclick chemistry for the synthesis of pyrazoles via 1,3‐dipolar cycloaddition between alkynes and nitrilimines generated in situ

Remy, Richard ; Bochet, Christian G.

In: European Journal of Organic Chemistry, 2018, vol. 2018, no. 3, p. 316–328

The photochemical extrusion of gaseous nitrogen from 2,5-disubstituted tetrazoles to generate reactive nitrilimines in situ represents an efficient and attractive way to form dipoles that can be used to provide useful chemicals via 1,3-dipolar cycloadditions. The concept of “photoclick chemistry” already inspired numerous researchers, who exploited photochemical processes involving...

Université de Fribourg

The Primary steps in excited-state hydrogen transfer: the phototautomerization of o-nitrobenzyl derivatives

Šolomek, Tomáš ; Bochet, Christian G. ; Bally, Thomas

In: Chemistry – A European Journal, 2014, vol. 20, no. 26, p. 8062–8067

The quantum yield for the release of leaving groups from o-nitrobenzyl “caged” compounds varies greatly with the nature of these leaving groups, for reasons that have never been well understood. We found that the barriers for the primary hydrogen-atom transfer step and the efficient nonradiative processes on the excited singlet and triplet surfaces determine the quantum yields. The...

Université de Fribourg

The photocycloaddition of arenes and allenes

Streit, Ursula ; Birbaum, Frédéric ; Quattropani, Anna ; Bochet, Christian G.

In: The Journal of Organic Chemistry, 2013, p. -

In the present work, we report on a new intramolecular para-cycloaddition of arenes with allenes, yielding attractive rigid scaffolds bearing several reactive functionalities to build in further diversity. Bicyclo[2.2.2]octadiene-type products and benzoxepine acetals are formed in this reaction, in ratios and yields depending on the substitution pattern on the aromatic ring, the nature of the...

Université de Fribourg

Photolysis of ortho-nitrobenzylic derivatives: the importance of the leaving group

Šolomek, Tomáš ; Mercier, Sébastien ; Bally, Thomas ; Bochet, Christian G.

In: Photochemical & Photobiological Sciences, 2012, vol. 11, no. 3, p. 548-555

Quantum yields for the photoinduced release of seven different commonly used leaving groups (LGs) from the o-nitroveratryl protecting group were measured. It was found that these quantum yields depend strongly on the nature of the LGs. We show that the quantum efficiency with which the LGs are released correlates with the stabilization that these LGs provide to o-nitrobenzyl-type radicals because...

Université de Fribourg

Singlet-Oxygen-Induced Rearrangement of Furan Derivatives

Charbonnet, Nicolas ; Riguet, Emmanuel ; Bochet, Christian G.

In: Synlett, 2012, vol. 15, p. 2231-2233

photochemistry; heterocycles; singlet oxygen; rearrangement; pyrroles; furans

Université de Fribourg

Wavelength-Selective caged surfaces: how many functional levels are possible?

Miguel, Vernica San ; Bochet, Christian G. ; Campo, Arnzazu del

In: Journal of the American Chemical Society, 2011, vol. 133, no. 14, p. 5380–5388

The possibility of wavelength-selective cleavage of seven photolabile caging groups from different families has been studied. Amine-, thiol-, and carboxylic-terminated organosilanes were caged with o-nitrobenzyl (NVOC, NPPOC), benzoin (BNZ), (coumarin-4-yl)methyl (DEACM), 7-nitroindoline (DNI, BNI), and p-hydroxyphenacyl (pHP) derivatives. Caged surfaces modified with the different chromophores...

Université de Fribourg

Total synthesis of the Amaryllidaceae alkaloid clivonine

Haninga, Helmut ; Giró-Mañas, Carles ; Paddock, Victoria L. ; Bochet, Christian G. ; White, Andrew J. P. ; Bernardinelli, Gerald ; Mann, Inderjit ; Oppolzer, Wolfang ; Spivey, Alan C.

In: Organic & Biomolecular Chemistry, 2011, vol. 9, p. 2809-2820

Two syntheses of the Amaryllidaceae alkaloid clivonine (1) are described. Both employ previously reported 7-arylhydrindane 6 as an intermediate but differ in the method employed for subsequent introduction of what becomes the ring-B lactone carbonyl carbon (C7). The synthesis featuring a Bischler–Napieralski reaction for this transformation constitutes the first asymmetric synthesis of natural...

Université de Fribourg

The arene–alkene photocycloaddition

Streit, Ursula ; Bochet, Christian G.

In: Beilstein Journal of Organic Chemistry, 2011, vol. 7, p. 525–542

n the presence of an alkene, three different modes of photocycloaddition with benzene derivatives can occur; the [2 + 2] or ortho, the [3 + 2] or meta, and the [4 + 2] or para photocycloaddition. This short review aims to demonstrate the synthetic power of these photocycloadditions.

Université de Fribourg

Preparation of photoactivable amino acid derivatives

Débieux, Jean-Luc ; Bochet, Christian G.

In: Journal of Organic Chemistry, 2009, vol. 74, no. 12, p. 4519–4524

A range of N-protected-α-amino acyl-5,7-dinitroindolines 3a−z were prepared in good yields from commercially available N-protected-α-amino acids 1a−z by a two-step sequence of acylation and intramolecular amide N-arylation. Subsequent photochemical acylation of the N-protected-α-amino acyl-5,7-dinitroindolines 3e,g,r afforded the corresponding N-protected-α-amino acid amides 22e,g,r...