Pyridoxal phosphate, the co-factor of many enzymes involved in aminoacid metabolism, has been found to undergo a rapid, benzoin type, selfcondensation in oxygen-free solution when exposed to light. The main product isolated was shown to be 5 : 5'-bis(dihydroxyphosphiny1oxymethy1) -3 : 3'-dihydroxy-2 : 2'-dimethyl-4 : 4'-pyridil, presumably formed from the corresponding pyridoin during working up in the presence of air.AQUEOUS solutions of pure crystalline pyridoxal phosphate monohydrate (I; X = CHO) were found to decompose rapidly when exposed to sunlight or irradiated with ultraviolet light. Dilute solutions (ca. 0.5%) in air-free water under nitrogen, exposed to strong summer sunlight in 100 ml. Pyrex flasks, were completely photolysed in one hour. Little difference in the rate of reaction was observed between pH 2.0 and pH 8.0.The photolysis was followed by measuring the ultraviolet absorption spectra of the solutions at pH 7.0 in phosphate buffer, the characteristic maximum of pyridoxal phosphate at 387 my being replaced by one of approximately equal intensity at 288 mp. In acid or in alkaline solution the difference between the spectra of pyridoxal phosphate and its photolysed solution was much less marked.By fractionation on a carboxylic acid ion-exchange resin, the principal product of the reaction was isolated in 75-88% yield, as colourless, high-melting crystals with an elementary analysis approximating to that of pyridoxal phosphate. It was almost insoluble in water and most organic solvents but dissolved readily in aqueous alkali to intensely yellow solutions.The presence of one carbonyl group per-atom of phosphorus in the molecule was established by preparing an oxime with a N : P ratio of 2 : 1. Whereas pyridoxal phosphate reacts rapidly with hydroxylamine at room temperature, the oxime of the photolysis product was formed only on several hours' boiling. The reactive 4-formyl group of pyridoxal phosphate had therefore been altered.

The redox-sensitive functionalities such as aliphatic amines with low oxidation potential which could be easily oxidized by the photocatalysts, are generally not compatible in photocatalytic reactions. We describe the visible...

Boron neutron capture therapy (BNCT) is a promising cancer treatment strategy that utilizes boron-containing ligands. In this report, a series of substituted boramino acids were synthesized and evaluated, aiming to obtain metabolically stable boron-derived agents that could integrate positron emission tomography (PET) with BNCT (a theranostic agent). Based on the phenylalanine (Phe) core structure, the impact of substitution groups on tumor accumulation was studied. The agents were labeled with fluorine-18 in 27.2−66.8% yield via the 18 F− 19 F isotope exchange reaction. In B16-F10 tumor-bearing mice,demonstrated the best tumor uptake (5.54 ± 2.32% ID/g based on ex vivo biodistribution and 3.5 ± 0.04% ID/g based on PET imaging with the tumor-to-muscle ratio up to 2.6) and stability compared with other tested agents. Together, R-[ 18 F]-5a is a promising agent that could potentially integrate PET and BNCT, whose treatment efficacy is worth further evaluation in the future.