Two series of nucleolipids, O-2',3'-heptanylidene- as well as O-2',3'-undecanylidene ketals of six β-d-ribonucleosides (type A) and partly N-farnesyl derivatives thereof (type B) were prepared in a combinatorial manner. All novel compounds were characterized by elemental analysis and/or ESI mass spectrometry and by UV-, H-, and C-NMR spectroscopy. Conformational parameters of the nucleosides and nucleolipids were calculated from various J(H,H), J( H, C), and J(F,H) coupling constants. For a drug profiling, the parent nucleosides and their lipophilic derivatives were studied with respect to their distribution (log P) between water and n-octanol as well as water and cyclohexane. From these data, qualitative conclusions were drawn concerning their possible blood-brain barrier passage efficiency. Moreover, nucleolipids were characterized by their molecular descriptor amphiphilic ratio (a.r.), which describes the balance between the hydrophilicity of the nucleoside headgroup and the lipophilicity of the lipid tail. All compounds were investigated in vitro with respect to their cytostatic/cytotoxic activity toward human glioblastoma (GOS 3) as well as rat malignant neuroectodermal BT4Ca cell lines in vitro. In order to differentiate between anticancer and side-effects of the novel nucleolipids, they were also studied on their activity on differentiated human THP-1 macrophages.

Two lipophilic derivatives of formycin A (1) and formycin B (5) carrying an O‐2′,3′‐(ethyl levulinate) ketal group have been prepared. These were base‐alkylated at N(1) (for 1) and N(1) and N(6) (for 5) with both isopentenyl and all‐trans‐farnesyl residues. Upon the prenylation, side reactions were observed, resulting in the formation of nucleolipids with a novel tricyclic nucleobase (→4a, 4b). In the case of formycin B, O‐2′,3′‐(ethyl levulinate) (6) farnesylation gave the double prenylated nucleolipid 7. All new compounds were characterized by 1H‐, 13C‐, UV/VIS and fluorescence spectroscopy, by ESI‐MS spectrometry and/or by elemental analysis. Log P determinations between water and octanol as well as water and cyclohexane of a selection of compounds allowed qualitative conclusions concerning their potential blood‐brain barrier passage efficiency. All compounds were investigated in vitro with respect to their cytotoxic activity toward rat malignant neuroectodermal BT4Ca as well as against a series of human glioblastoma cell lines (GOS 3, U‐87 MG and GBM 2014/42). In order to differentiate between anticancer and side effects of the novel nucleolipids, we also studied their activity on PMA‐differentiated human THP‐1 macrophages. Here, we show that particularly the formycin A derivative 3b possesses promising antitumor properties in several cancer cell lines with profound cytotoxic effects partly on human glioblastoma cells, with a higher efficacy than the chemotherapeutic drug 5‐fluorouridine.

2‐Chloro‐2′‐deoxyadenosine (cladribine, 1) was acylated with valproic acid (2) under various reaction conditions yielding 2‐chloro‐2′‐deoxy‐3′,5′‐O‐divalproyladenosine (3) as well as the 3′‐O‐ and 5′‐O‐monovalproylated derivatives, 2‐chloro‐2′‐deoxy‐3′‐O‐valproyladenosine (4) and 2‐chloro‐2′‐deoxy‐5′‐O‐valproyladenosine (5), as new co‐drugs. In addition, 6‐azauridine‐2′,3′‐O‐(ethyl levulinate) (8) was valproylated at the 5′‐OH group (→9). All products were characterized by 1H‐ and 13C‐NMR spectroscopy and ESI mass spectrometry. The structure of the by‐product 6 (N‐cyclohexyl‐N‐(cyclohexylcarbamoyl)‐2‐propylpentanamide), formed upon valproylation of cladribine in the presence of N,N‐dimethylaminopyridine and dicyclohexylcarbodiimide, was analyzed by X‐ray crystallography. Cladribine as well as its valproylated co‐drugs were tested upon their cancerostatic/cancerotoxic activity in human astrocytoma/oligodendroglioma GOS‐3 cells, in rat malignant neuro ectodermal BT4Ca cells, as well as in phorbol‐12‐myristate 13‐acetate (PMA)‐differentiated human THP‐1 macrophages. The most important result of these experiments is the finding that only the 3′‐O‐valproylated derivative 4 exhibits a significant antitumor activity while the 5′‐O‐ as well as the 3′,5′‐O‐divalproylated cladribine derivatives 3 and 5 proved to be inactive.

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The lipophilization of β‐d‐riboguanosine (1) with various symmetric as well as asymmetric ketones is described (→3a–3f). The formation of the corresponding O‐2′,3′‐ketals is accompanied by the appearance of various fluorescent by‐products which were isolated chromatographically as mixtures and tentatively analyzed by ESI‐MS spectrometry. The mainly formed guanosine nucleolipids were isolated and characterized by elemental analyses, 1H‐, 13C‐NMR and UV spectroscopy. For a drug profiling, static topological polar surface areas as well as 10logPOW values were calculated by an increment‐based method as well as experimentally for the systems 1‐octanol‐H2O and cyclohexane‐H2O. The guanosine‐O‐2′,3′‐ketal derivatives 3b and 3a could be crystallized in (D6)DMSO – the latter after one year of standing at ambient temperature. X‐ray analysis revealed the formation of self‐assembled ribbons consisting of two structurally similar 3b nucleolipid conformers as well as integrated (D6)DMSO molecules. In the case of 3a ⋅ DMSO, the ribbon is formed by a single type of guanosine nucleolipid molecules. The crystalline material 3b ⋅ DMSO was further analyzed by differential scanning calorimetry (DSC) and temperature‐dependent polarization microscopy. Crystallization was also performed on interdigitated electrodes (Au, distance, 5 μm) and visualized by scanning electron microscopy. Resistance and amperage measurements clearly demonstrate that the electrode‐bridging 3b crystals are electrically conducting. All O‐2′,3′‐guanosine ketals were tested on their cytostatic/cytotoxic activity towards phorbol 12‐myristate 13‐acetate (PMA)‐differentiated human THP‐1 macrophages as well as against human astrocytoma/oligodendroglioma GOS‐3 cells and against rat malignant neuroectodermal BT4Ca cells.