Four oleyl or dolichyl thiophosphate esters 16, 17, 21, and 22, analogues of Dol-P-Man possessing C(1)S and/or PS bonds, were synthesized as potential inhibitors of mannosyl transferases operating in the endoplasmic reticulum (ER). The β-mannosyl derivatives were prepared by a Mitsunobu reaction of 2,3,4,6-tetra-O-acetyl-α-D-mannopyranose (1) with the thiophosphate 2 that provided O- and S-glycosides