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The synthesis of four CD-ring-modified 19-nor-1alpha, 25-dihydroxyvitamin D(3) derivatives lacking C15, referred to as 6C analogues, and diastereomeric at C17 and C20 is described. The synthesis involves an Ireland-Claisen rearrangement of a 3-methyl-substituted ester of (1R)-3-methyl-2-cyclohexen-1-ol as the key step, followed by elaboration of the side chain, transformation into a C8 cyclohexanone derivative, and final Wittig-Horner coupling with the 19-nor A-ring phosphine oxide. Despite possessing a more flexible side chain than the parent hormone, biological evaluation showed an unexpected superagonistic antiproliferative and prodifferentiating activity (10-50 times higher as compared to that of 1alpha,25(OH)(2)D(3)) for the diastereomer with the "natural" configuration at C17 and C20. The other diastereomers exhibit a 25-90% decrease in activity. All four analogues show a decreased binding affinity (45% or less), and their calcemic activity is 4-400 times less than that of 1alpha,25(OH)(2)D(3). The conformational behavior of their side chain was studied using molecular mechanics calculations, and the result is presented as volume maps. A relative activity volume was determined by subtraction of the volume map of the least active analogue from the volume map of the most active one. This shows three regions corresponding to preferred orientations in space of the side chain of the active analogue. One of these regions was found to overlap with the region that is preferentially occupied by the most active of the four diastereomeric 22-methyl-substituted 1alpha,25(OH)(2)D(3) analogues.

Two conceptually attractive enantioselective syntheses of (+)-biotin from L-cysteine are reported based upon an intramolecular 1,3-dipolar cycloaddition of a carbamoyl azide. The first approach (12 steps) involves the following as key-steps: (i) the macrothiolactonization of acid 10b to Z-olefin 14, (ii) the thermolysis of the ene carbamoyl azide 15 in water with direct formation of a mixture of the benzylated derivatives of (+)-biotin 16a and 17a. The second approach (14 steps) involves the following: (i) elimination of bromide 29 to the endocyclic thioenol ether 30, (ii) thermolysis of the ene carbamoyl azide 30 to the exocyclic thioenol ethers 31a and 31b. Both the synthesis of 29 and the final transformation of 31a and 31b into (+)-biotin are based upon literature precedents.