Cyclodextrin-benzaldehyde inclusion complexation

Irradiation of solid 1 1 complexes of benzaldehyde 89 and P-cyclodextrin 2 resulted in enantioselective intermolecular hydrogen abstraction and radical coupling to afford (/ )-( — )-benzoin 90 as a major product in up to 15% ee and 56% chemical yield. 4-Benzoylbenzaldehyde was obtained as a minor product (Scheme 20) [22]. This reactivity can be understood from the presence of guest-to-host (2 2) complexes generated by the head-to-head association of two 1 1 inclusion complexes. 

A direct solution to the problem of enantioselective furan-carbonyl photoproduct synthesis would require a photoaddition that proceeded with enantiofacial selectivity in the aldehyde or furan component and maintained the relative face selectivity that is intrinsic to the reaction. Preliminary work used host-guest chemistry to achieve this objective.In aqueous dioxane, a 1 1 1 inclusion complex of unmodified 3-cyclodextrin, furan and benzaldehyde is formed. Upon irradiation (Hanovia 450 W lamp, Vycor filter), a rapid photoaddition occurs to afford a photoproduct of 10-20% ee. 

AUTOXIDATIQN The autoxidadon rates of free benzalddiyde and its inclusion complex with a-cyclodextrin in neutral solution at 7(fC were measured by HPLC. The half-life for die a-cyclodextrin-benzaldehyde was 62 hr., 3.6 times longer than that for benzaldehyde alone (1.7 hr.), indicating that the aldehyde group is included into the cyclodextrin cavity whidi prevents oxidation by air. 

ANTITUMOR CYTOTOXICITY The stabilization effect of benzaldehyde by a-cyclodextrin is also reflected in the in vitro antitumor cytotoxicity against human tumor cell lines A-549 (non-small-cell lung carcinoma), MCF-7 (breast adenocarcinoma) and HT-29 (colon adenocarcinoma) (Table III). a-Cyclodextrin-benzaldehyde inclusion complex is about 5-8 fold more cytotoxic than ftee ben dehyde. 

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