- Enantioselective C-H Lactonization of Unactivated Methylenes Directed by Carboxylic Acids
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The formidable challenges of controlling site-selectivity, enantioselectivity, and product chemoselectivity make asymmetric C-H oxidation a generally unsolved problem for nonenzymatic systems. Discrimination between the two enantiotopic C-H bonds of an unactivated methylenic group is particularly demanding and so far unprecedented, given the similarity between their environments and the facile overoxidation of the initially formed hydroxylation product. Here we show that a Mn-catalyzed C-H oxidation directed by carboxylic acids can overcome these challenges to yield γ-lactones in high enantiomeric excess (up to 99%) using hydrogen peroxide as oxidant and a Br?nsted acid additive under mild conditions and short reaction times. Coordination of the carboxylic acid group to the bulky Mn complex ensures the rigidity needed for high enantioselectivity and dictates the outstanding γsite-selectivity. When the substrate contains nonequivalent γ-methylenes, the site-selectivity for lactonization can be rationally predicted on the basis of simple C-H activation/deactivation effects exerted by proximal substituents. In addition, discrimination of diastereotopic C-H bonds can be modulated by catalyst design, with no erosion of enantiomeric excess. The potential of this reaction is illustrated in the concise synthesis of a tetrahydroxylated bicyclo[3.3.1]nonane enabled by two key, sequential γ-C-H lactonizations, with the latter that fixes the chirality of five stereogenic centers in one step with 96% ee.
- Cianfanelli, Marco,Olivo, Giorgio,Milan, Michela,Klein Gebbink, Robertus J. M.,Ribas, Xavi,Bietti, Massimo,Costas, Miquel
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supporting information
p. 1584 - 1593
(2020/02/04)
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- Tumor-cell-targeted methionine-enkephalin analogues containing unnatural amino acids: Design, synthesis, and in vitro antitumor activity
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A series of new peptides (8-25) containing different unnatural amino acids of the adamantane type (1-6), was synthesized. Possible cytotoxic activity on human cervical adenocarcinoma (HeLa), larynx carcinoma (HEp-2), colon carcinomas (HT-29, Caco-2), poorly differentiated cells from lymph node metastasis of colon carcinoma (SW-620), mammary gland adenocarcinoma (MCF-7), and melanoma (HBL) cells were tested by the MTT assay. The results were compared with the effect of methionine-enkephalin (Tyr-Gly-Gly-Phe-Met, or opioid growth factor, OGF), and its shorter N-terminal fragments. Peptide analogues containing Cαα-dialkylated glycine (Aaa1, 1) or Cα-alkylated glycine (Aaa2, 2) amino acid residues showed antitumor activity against melanoma, larynx carcinoma, colon carcinomas, and colon metastasis cell lines in vitro. The pentapeptide Tyr-(R,S)-Aaa2-Gly-Phe-Met (18) was the most effective analogue especially against the most antitumor drug-resistant cell lines HEp-2 and SW-620. Apoptosis as a mode of cell death was confirmed in these tumor cells after exposure to pentapeptide 18.
- Horvat, ?tefica,Mlinari?-Majerski, Kata,Glava?-Obrovac, Ljubica,Jakas, Andreja,Veljkovi?, Jelena,Marczi, Sa?ka,Kragol, Goran,Ro??i?, Maja,Matkovi?, Marija,Milosti?-Srb, Andrea
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p. 3136 - 3142
(2007/10/03)
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- SYNTHESIS AND CHEMICAL TRANSFORMATIONS OF ACETYLAMINO DERIVATIVES OF ADAMANTANE
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The synthesis of acetylamino derivatives of adamantane by the Ritter reaction in a mixture of sulfuric and nitric acids is described.Their hydrolysis in the presence of hydrochloric acid was investigated.
- Novikov, S. S.,Khardin, A. P.,Butenko, L. N.,Kulev, I. A.,Novakov, I. A.,et al.
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p. 1231 - 1232
(2007/10/02)
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