F. Pietra

Relative Contributions to Antitumoral Activity of Lipophilic vs. Polar Reactive Moieties in Marine Terpenoids

Marked cytotoxicity of norsesterterpenoids 3 and 4 vs. inactivity or low activity of the respective norditerpenoid analogues 2 and 1 towards KB tumoral cell lines suggest that the length of the lipophilic chain is an important factor while, per se the reactive peroxide functionality is not. Moreover, lower bioactivity towards the same cells of 1 than 2, and comparable activities of 3–5, show the unimportance per se of the highly electrophilic enone moiety. A strict need of molecular tailoring, so that weapons may reach the target in adaptive phenomena, may be at the basis of natural selection of these compounds and suggests strategies for the design of safer agents against cancer.

Hemithio-analogues of meisenheimer complexes and sulphide group activation of aromatic substitution by alkoxides

Abstract EtO− in DMSO adds to ethylthiopicrate at C-3 to generate an ephemeral -adduct which ends into 1-ethylthio-4-ethoxy-2,5-dinitrobenzene, whilst ethyl picrate gives two adducts of attack of EtS− at C-3 or C-1.

The relative reactivity of fluoro- and chloro-2,4-dinitrobenzenes in their reactions with amines

Francesco Pietra Istituto di Chimica Generale, Universita di Pisa, Pisa, Italy. (Received 1 February 1965) Although the leaving group ability of fluoride relative to other halide ions in nucleophilic activated aromatic substitution reactions has received considerable attention (1), there is still much controversy about the factors governing it. In the course of a kinetic investigation of the reactions of activated aryl halides with amines in non-polar aprotic solvents, a preliminary account of, which has already been given (2), data have been collected which appear to be relevant to the above mentioned problem. These concern the reactions of fluoro-2,4-dinitrobenzene (FDNB) or chloro-2,4dinitrobenzene (CDNB) with piperidine, 2-methylpiperidine and cis-2,6_dimethylpiperidine respectively in benzene at 25’. In Table I are listed the data for the reactions of the last two aminesr those for piperidine have already been reported (2). Examination of the results for the reactions of FDNB (Table Ia, Ib) shows that the second-order rate coefficients increase with increasing amine concentration. The rate data can be very satisfactorily expressed by equation [1]

Chemistry of a meisenheimer-type σ-adduct derived from a troponoid

Abstract The gem-dimethoxy σ-adduct of methoxide addition to 2-methoxy-3-nitro-4,5-benzotropone reacts with either (C 2 H 5 ) 3 OBF 4 , to change the nitronate into an oxime function, or (CH 3 ) 3 SiCl, to give 2-carbomethoxy-1-nitronaphthalene and the nitronic acid corresponding to the starting adduct.

On the ortho : para ratio in activation of nucleophilic aromatic substitution by the nitro-group

Contrary to recent criticism, previously obtained high ortho : para ratios in activation of nucleophilic aromatic substitution by nitro-group prove to be genuine.