| Popis: |
The synthesis of two new A-ring precursors, useful for the convergent assembly of 2α-ethyl and 2β-ethyl derivatives of 19-nor-1α,25-dihydroxyvitamin D3, is described. These building blocks were prepared in 14 steps from quinic acid, which led to a new and practical synthesis of 2α-ethyl-14-epi-19-nor-20-epi-23-yne-1,25(OH)2D3, an analog that shows a remarkably low calcemic effect in mice, while retaining the ability to promote cell differentiation and to inhibit cell proliferation in a number of human cancer cell lines. |
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