In most sunscreens, the presence of two UV filters usually leads to synergistic effects regarding both the final performance and photostabilization of the active principles. However, this may also result in an accelerated decomposition if a photoreaction occurs between the single components. Thus, the understanding of photophysics and photochemistry of UV filter combinations is important to improve sunscreen photostability. In this context, photoreactivity of a commonly used UVA filter, namely tert-butylmethoxydibenzoylmethane (BM-DBM, also known as avobenzone, Parsol 1789, etc.), has been studied in the presence of six commercial solar filters: octyl methoxycinnamate, bis-ethylhexyloxyphenol methoxyphenyl triazine, octocrylene, diethylamino hydroxybenzoyl hexyl benzoate, octyl triazone and dioctyl butamido triazone. To achieve this goal, a mechanism-based strategy has been designed in order to investigate the photostability of sunscreens in a more systematic way, taking into account different processes: tautomerization of BM-DBM, formation of triplet excited state of BM-DBM in its diketo form and its quenching in the presence of UV filters, reactivity of UV filters under triplet photosensitization, quenching of singlet oxygen by UV filters and degradation of the latter under singlet oxygenation conditions.

Novel sunscreens are required providing active protection in the UVA and UVB regions. On the other hand, there is an increasing concern about the photosafety of UV filters, as some of them are not sufficiently photostable. Avobenzone is one of the most frequently employed sunscreen ingredients, but it has been reported to partially decompose after irradiation. In the present work, photophysical and photochemical studies on a methylated avobenzone-derivative have shown that the diketo form is responsible for photodegradation. A transient absorption was observed at 380 nm after laser flash photolysis excitation at 308 nm. It was assigned to the triplet excited state of the diketo form, as inferred from quenching by oxygen and b-carotene. This transient also interacted with key building blocks of biomolecules by triplet-triplet energy transfer (in the case of thymidine) or electron transfer processes (for 2¢-deoxyguanosine, tryptophan and tyrosine). Irradiation of the avobenzone derivative in the presence of a triazine UV-B filter (E-35852) diminished the undesirable effects of the compound by an efficient quenching of the triplet excited state. Thus, sunscreen formulations including triplet quenchers could provide effective protection from the potential phototoxic and photoallergic effects derived from poor photostability of avobenzone.

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Just add CH3CN and stir! Four building blocks taken in a multicomponent reaction (MCR, see picture; Tf=trifluoromethanesulfonyl) afford a β‐aminoacetal adduct, which can be further diversified by post‐condensation reactions. The modular character of this approach, the simplicity of the building blocks used, and the structural diversity attained render this process attractive for combinatorial as well as target‐ and diversity‐oriented synthesis.

A multicomponent assembly of pyrido-fused tetrahydroquinolines is accomplished in a one-pot process from the interaction of dihydroazines, aldehydes, and anilines. A rational screening of the different components and parameters of this reaction, such as the range of reactive starting materials, catalysts and reaction conditions (solvent range; thermal, high pressure- and microwave-promoted processes) is carried out. Optimized conditions allow an efficient preparation of pyrido-fused tetrahydroquinolines with good yields, bypassing the biomimetic NADH-like reductive pathway which is typical in the interaction of dihydropyridines with carbonyl compounds and amines. Furthermore, solid-supported versions of the process have been developed, which should facilitate the preparation of libraries.