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The photolysis of α-methoxy acetophenones 1a–1eadsorbed on silica gel show a significant deviation from the course of reaction in methanol. The results are discussed in terms of conformational control and restricted movement of the radical through adsorption on silica gel. Factors affecting the efficiency of modification of photochemical reactivity on silica gel surface have been examined.

Retinoids serve as physiologic and pharmacologic mediators of proliferation, differentiation and apoptosis in normal and malignant cell types. All-trans-retinoic acid (tRA), a natural metabolite of vitamin A, induces differentiation and subsequent apoptosis in several types of malignant cells with immature phenotypes. Clinically, tRA has been approved for the treatment of patients with acute promyelocytic leukemia. Several synthetic retinoids induce apoptosis without differentiation in a variety of malignant epithelial cells in vitro. The synthetic derivative, N-(4-hydroxyphenyl)retinamide (HPR), shows significant promise as a chemo-preventive and therapeutic anti-cancer agent in light of its minimal toxicity and broad activity in experimental cancer models representing common human malignancies. This paper reviews the role of retinoids as mediators of differentiation and apoptosis in malignant cells, and the impact this activity could have on clinical oncology.

Dianin's compound (4-p-hydroxyphenyl-2,2,4-trimethylchroman) serves as host in a series of well-defined clathrate inclusion complexes with eleven linear, as well as branched chain, phenyl alkyl ketone guest molecules, chosen for their ability to undergo the Norrish type I and type II photochemical reactions in solution. The photochemical reactivity of the guest ketones within the clathrate cavity was determined by irradiation of the inclusion complexes in the solid state. The results were compared to the photoreactivity of the ketones in polar as well as nonpolar liquid media. In general, the inclusion complex medium brings about an enhancement of type I over type II reactivity and causes an increase in type II fragmentation compared to type II cyclization. This change in reactivity is interpreted as resulting from the relatively restricted environment of the clathrate cavity coupled with the greater motion required for the type II process (γ-hydrogen abstraction) compared to the type I reaction (α-cleavage), as well as from the greater steric requirements for type II cyclization (cyclobutanol formation) as compared to type II cleavage (1,4-hydroxybiradical scission).