3′-Deoxyformycin was prepared by transformation of the formycin A with 2-acetoxyisobutyryl bromide. Both formycin A and its 3′-deoxy analogue were converted into their 5′-chloro-5′-deoxy derivatives with thionyl chloride. Finally 5′-chloro-5′-deoxy formycin A and 5′-chloro-3′,5′ dideoxyformycin A were condensed with L-homocysteine sodium salt to give S-formycinyl-L-homocysteine and S-3′-deoxyformycinyl-L-homocysteine in good yields.