With best personal wishes dedicated to Prof. Dr. Albert Eschenmoser on the occassion of his 75th birthday The syntheses of the 3'-O-(4,4'-dimethoxytrityl)-protected 5'-phosphoramidites 25 ± 28 and 5'-(hydrogen succinates) 29 ± 32, which can be used as monomeric building blocks for the inverse (5'-3')-oligodeoxyribonucleotide synthesis are described (Scheme). These activated nucleosides and nucleotides were obtained by two slightly different four-step syntheses starting with the base-protected nucleosides 13 ± 20. For the protection of the aglycon residues, the well-established 2-(4-nitrophenyl)ethyl (npe) and [2-(4-nitrophenyl)ethoxy]carbonyl (npeoc) groups were used. The assembly of the oligonucleotides required a slightly increased coupling time of 3 min in application of the common protocol (see Table ). The use of pyridinium hydrochloride as an activator (instead of 1H-tetrazole) resulted in an extremely shorter activation time of 30 seconds. We established the efficiency of this inverse strategy by the synthesis of the oligonucleotide 3'-conjugates 33 and 34 which carry lipophilic caps derived from cholesterol and vitamin E, respectively, as well as by the formation of (3'-3')-and (5'-5')-internucleotide linkages (see Table ). Scheme