The first boranothiotriphosphate compound, thymidine 5′-[α-P-borano, α-P-thio]triphosphate, in which borane and sulfur replace the two non-bridging oxygens of the α-phosphate in natural nucleoside triphosphates (NTPs), has been synthesized; some chemical properties of this borane–sulfur disubstituted nucleoside triphosphate analogue have been investigated. The synthetic approach reported here should be applicable for preparation of any α-borano, α-thio modified NTP or deoxy NTP; potential applications are discussed.