Amygdalin (d-Mandelonitrile 6-O-β-d-glucosido-β-d-glucoside) is a natural cyanogenic glycoside occurring in the seeds of some edible plants, such as bitter almonds and peaches. It is a medically interesting but controversial compound as it has anticancer activity on one hand and can be toxic via enzymatic degradation and production of hydrogen cyanide on the other hand. Despite numerous contributions on cancer cell lines, the clinical evidence for the anticancer activity of amygdalin is not fully confirmed. Moreover, high dose exposures to amygdalin can produce cyanide toxicity. The aim of this review is to present the current state of knowledge on the sources, toxicity and anticancer properties of amygdalin, and analytical methods for its determination in plant seeds.
Treatment of 1,8-bis(diphenylphosphino)naphthalene (1) with borane-dimethyl sulfide complex in THF/Et 2 O solution affords monoborane adduct 3 irrespective of the molar ratio of the reagents. The monoboronation product has been characterized by multinuclear ( 1 H, 31 P, 13 C, 11 B) NMR spectroscopy and MS-FAB measurements. Optimization of its structure with DFT methods at the B3LYP/6-31þG(d) level of theory revealed that steric hindrance around the diphenylphosphino group prevents formation of the bis-borane adduct. In dichloromethane or chloroform solution boronation of bis-phosphine 1 with H 3 B 3 Me 2 S results in the unexpected formation of a cyclic dihydroboronium chloride, 4 3 Cl. The corresponding cyclic iodide 4 3 I and triflate 4 3 TfO are formed by treatment of bis-phosphine 1 with H 3 B 3 Me 2 S followed by methyl iodide and methyl triflate, respectively, in THF/Et 2 O solution. The hexafluorophosphate 4 3 PF 6 prepared by anion exchange from the chloride 4 3 Cl has also been characterized by single-crystal X-ray diffraction. It has been demonstrated that the cyclic boronium salts are formed in two steps. The first is the formation of monoborane adduct 3, which in the second step undergoes cyclization with concomitant reduction of the chlorohydrocarbon solvents, methyl iodide or triflate. Some aspects of this unprecedented reductive cyclization have been elucidated by DFT calculations. ^Dedicated to Prof. Marek Zaidlewicz on the occasion of his 70th birthday.
The first solvent- and catalyst-free procedure for the Michaelis–Arbuzov reaction under flow conditions was developed. A variety of alkylphosphonic esters could be obtained using this protocol starting from the corresponding trialkyl phosphites and even catalytic amounts of alkyl halides with very short reaction times (8.33–50 min) and excellent conversions. In general, this protocol works effectively when the alkyl halide is used in catalytic amounts as low as 5–10% only if it concerns the synthesis of homo alkylphosphonates. One equivalent and an excess of alkyl halides should be used in the reaction with alkyl phosphite if the alkyl group of the selected substrates differ. Thus, it provides a sustainable, fast alternative to the existing methods for the preparation of alkylphosphonates. The isolation of the reaction products is straightforward due to the lack of solvents and a high purity of the obtained products (conv ≥ 99%), and notably, in the catalytic procedures there are only traces of alkyl halides formed after the reaction is complete. The reactions conducted using a glass microreactor chip with an internal volume of 250 μL allow the production of 1.6–1.95 g of organophosphorus esters per hour.
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