Sila Analogues

properties.

7,22,148,210,218 225

Some trimethylsilyl derivatives of retinobenzoic acids show high retino-idal activity in human promyelotic leukaemia cells HL-60.224,236 Thus, (E)-4-{3-[3,5-bis(trimethylsilyl)phenyl]-3-oxo-1-propenyl}benzoic acid (17b) is one order of magnitude more potent than retinoic acid. It shows an activity similar to that of the carbon analogue 17a.224 If only one R3M group exists in the meta-position, the silicon derivative is more active than the carbon analogue but inferior to retinoic acid in activity, whereas in the case of para-substituted chalcones the substitution of a t-butyl group for trimethylsilyl leads to complete loss of activity. Me3M-substituted retinobenzoic acids 18 (M = C, Si), with an amide group between the aromatic rings, possess similar retinoidal activities. At the same time, in the pair of isomeric amides 19, the trimethylsilyl derivative 19b was five times more active than the carbon analogue 19a.224

4-[3,5-Bis(trimethylsilyl)benzamido]benzoic acid (TAC-101) has significant anti-metastatic and life-prolonging effect in a model of experimental liver metastasis of human gastric cancer cell line AZ-521.237,238 It also shows some efficacy in the prevention of experimental liver metastasis of colon cancer in mice, which was associated with the induction of apoptopic cell death and suppression of cancer cell invasion.239 TAC-101 was found to be an orally active anti-angiogenic agent and it has been suggested that this anti-angiogenic property may contribute to its efficacy against liver metastasis of human stomach cancer cells.240,241 Based on high efficacy in several animal mod-els,240 248 a clinical trial of TAC-101 was started in patients with cancer.241

Additionally, TAC-101 suppressed the onset and development of collagen-induced arthritis in mice and experimental autoimmune encephalomyelitis.249

The silicon analogues of the insecticides etofenprox (20a) and MTI-800 (21a) were slightly less toxic to insects (Mexican bean beetle, cabbage looper, pea aphid, American cockroach) than the carbon analogues.250 253 The compounds 21 with a methylene group instead of oxygen and fluorine at the 4-position of phenoxyphenyl were more active than compounds 20, but the most important property of 4-ethoxyphenyl-[3-(4-fluoro-3-phenoxyphenyl)propyl]dimethyl-silane (insecticide Silafluofen 21b) in contrast to pyrethroids is its negligible fish toxicity.250

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