Vitamin D.sub.3 analogues of the formula (I): ##STR1## wherein R.sub.1 is hydrogen or hydroxy, R.sub.2 is (C.sub.1 -C.sub.3)alkyl, hydroxy(C.sub.1 -C.sub.3)alkyl, (C.sub.1 -C.sub.2)alkoxymethyl, (C.sub.2 -C.sub.3)alkenyl, or (C.sub.2 -C.sub.3)alkynyl, R.sub.3 is a branched or unbranched, saturated or unsaturated aliphatic 3- to 5- membered hydrocarbon or oxahydrocarbon biradical, having at least 3 atoms in the main chain and being optionally substituted with one or more substituents selected from epoxy, fluoro and hydroxy, R.sub.4 is sec. or tert. (C.sub.3 -C.sub.6)alkyl or (C.sub.3 -C.sub.6)cycloalkyl, A and B are each individually hydrogen or methyl, or A and B together from methylene. The compounds of the present invention exhibit pharmacotherapeutic activities, including in particular, the treatment of osteoporosis, renal osteodystrophy, osteomalacia, skin disorders such as psoriasis and other hyperproliferative skin diseases, eczema and dermatitis, nmyopathy, leukemia, breast and colon cancer, osteosarcomas, squamous cell carcinomas, melanoma, certain immunological disorders, and transplant rejections. Several methods of synthesis, including reaction of an ester compound of general formula (IX) with an inorganometallic compound of formula (III) followed by deprotection or, alternatively, first finalization of the C.sub.17 -side chain are also disclosed.