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Apoptosis is an essential factor in keeping homeostasis of the organism. Apoptosis is regulated by a series of cytokines. Bcl-2 family proteins are key regulators of apoptosis. The Bcl-2 family includes both anti- and pro-apoptotic proteins with opposing biological functions. Their interaction regulates the transmission of the apoptosis signal. High expression of anti-apoptotic members such as Bcl-2 and Bcl-xL are commonly found in human cancers. In recent years, following the disclosing of the crystal structures of Bcl-2 family proteins, researchers have paid attention to the development of the small molecule inhibitors of Bcl-2 family proteins. This article reviews the progress in this field from the view of drug design.

The polymorphism of gossypol has been investigated by IR spectrophotometry and X-ray diffraction. Nine samples of gossypol crystallized from mixed solvent of ether, ethanol and water (1:2:2), five samples from chloroform and ten samples from petroleum ether (bp 60-90 degrees C) were determined. Significant differences in the infrared spectra of gossypol crystallized from three solvents were observed near 3500 cm-1. The spectrum of gossypol crystallized from mixed solvent of ether, ethanol and water (mp 183-184 degrees C) showed bands at 3500 (sh), 3470, 3375 cm-1; that from chloroform (mp 198-199 degrees C) at 3455, 3415 (sh) cm-1 and that from petroleum ether (mp 213-214 degrees C) at 3510, 3495, 3430 (sh), 3410 cm-1. Moreover, the spectra of the three forms of gossypol showed slightly different bands at 780 and 600-400 cm-1. Gossypol crystallized from the three solvents showed the same infrared spectra after being crystallized from acetone. Significant differences in the X-ray diffraction pattern of gossypol crystallized from the three solvents were also observed. Angles, intensities and D-values of most of the X-ray diffraction peaks were listed.

Fifteen condensates of chiral amines and racemic gossypol were prepared. Their 1HNMR spectra indicated that all the amine condensates tested had the same keto-enamine structures and shifts of protons on C11, C11 of various condensates were analyzed for their structural relationship. The Rf and delta Rf values (difference between (+) and (-)gossypol condensates) on TLC of these derivatives and stability of eight condensates of (-)gossypol were examined. All these properties were discussed in light of the configuration of gossypol. These studies not only provided rational basis of selecting resolving agent, but also gave indications of their relative absorbability and stereochemistry of the condensates which might be useful in postulating their in vivo behaviors and designing derivatives with better pharmacological actions.

A simplified and more practical method for the resolution of racemic gossypol was developed by quick chromatographing the condensation products of either (S) or (R)-alpha-methylphenethylamine and alpha-methylbenzylamine with racemic gossypol on a silica column using diethylether/light petroleum as eluent. The optically active gossypol thus obtained showed specific rotation [alpha]D of (+) or (-)370 +/- 10 degrees, with ee% 96.8 and 98.8 respectively and chemical purity greater than 99% by HPLC. Isomerization of the amino condensates of optically active gossypol through the racemization of the binaphthalene moiety of gossypol was observed, though gossypol itself is optically stable in such condition. The rate of racemization varied with the structure of the amine moiety and solvent present and was increased by light and free radical initiator.

Threo (-) or (+)-1-(p-nitrophenyl)-1,3-dihydroxypropylamine-2 was found to be a useful resolving agent for racemic gossypol. The optical and chemical stability of the condensate of enantiomeric gossypols with the titled amine and the great difference in the Rf values on TLC and the solubilities in various solvents between the two diastereoisomeric condensates facilitate the separation. Therefore, the pure isomers can be easily obtained by means of chromatography or crystallization.