Patent GB-753567-A (GB)
Title: Synthesis of nucleoside esters of pyrophosphoric acid
Inventor: TODD ALEXANDER ROBERTUS
IPC: C07H1/02
Filed: 1952-11-17
Abstract: The invention comprises nucleoside esters of phosphorous and halophosphonic acids, and the synthesis of nucleoside pyrophosphates therefrom as set out below, in which R1 and/or R2 is a nucleoside residue, the other being a monovalent hydrocarbon residue as also are R3 and R4. A phosphite mono-ester (R3O)(HO) PHO is treated with ZPO(OR4)2 in the presence of a tertiary base to give a phosphite-phosphate "mixed anhydride" (R3O)(PHO)O(PO)(OR4)2. Treatment of the latter with a nucleoside R1OH (protected if necessary) with a halogenating agent in an indifferent solvent in the presence of a tertiary base gives a halophosphonate ester (R1O)(R3O)(PO)X.  This is reacted with an orthophosphate mono-salt in which the other two hydrogen atoms may be replaced, one by a group R2 and the other by a protecting group where necessary, and the resulting pyrophosphate ester hydrolysed to split off the group R3 and any protecting groups in the phosphate or nucleoside portions of the molecule. The final product is (R1O)(HO)(PO)O(PO)(OH) (OR2). Preferably R3 is aralkyl, R4 is aryl and Z is halogen or (R4O)2(PO)-O-.  The halogenating agent is preferably an N-chloro secondary amide such as N-chloro-succinimide or N : 2 : 4-trichloracetanilide.  The chlorophosphonates so obtained may be characterized by hydrolysis to nucleotide esters or by treatment with amines to give aminophosphonates.  The orthophosphate may be used as a metallic, ammonium or substituted ammonium salt such as that of triethylamine.  Aralkyl protecting groups may be removed by treatment with a metallic or substituted ammonium salt (e.g. lithium chloride), or an alkali thiocyanate in a cyanoalkane, or by a phenol which has been used as solvent in the previous stage, or else by hydrogenolysis.  Protecting groups on the nucleoside residue (e.g. O-acyl or isopropylidene) can be split off by careful acid or alkaline hydrolysis.  In the examples: (1) monobenzyl phosphite (by acidification of its ammonium salt) is treated with diphenyl chlorophosphate or tetraphenyl pyrophosphate to give a mixed anhydride (characterized by reaction with ammonia and benzyl alcohol to form dibenzyl aminophosphonate); this with 21 : 31-isopropylidene-uridine yields 21 : 31 - isopropylidene - uridine - 51 - benzyl phosphite, converted by N-chlorsuccinimide into the 51-benzylchlorophosphonate (characterized by hydrolysis to 21 : 31-isopropylideneuridine - 51 - benzylhydrogenphosphate); this is reacted with triethylammonium 21 : 31-isopropylidene-51-benzylphosphate and the product debenzylated with potassium thiocyanate in acetonitrile; hydrolysis with hydrochloric acid gives di - (uridine - 51) - pyrophosphate, obtained as barium salt and converted via the free acid into the lithium salt; uridine-51-phosphate is a by-product; (2) 21 : 31-isopropylidene - uridine - 51 - benzylchlorophosphonate and triethylammonium dibenzyl phosphate give 21 : 31-isopropylidene-uridine-51-tri benzylpyrophosphate, converted by heating with lithium chloride into the lithium salt of 21 : 31 - isopropylidene - uridine - 51 - benzyl pyrophosphate; this is acidified and hydrogenated to uridine-51-pyrophosphate (obtained as barium salt) together with its 21 : 31-isopropylidene derivative and uridine-51-phosphate; (3) the mixed anhydride of (1) is reacted with 21 : 31 - diacetyl - uridine to give 21 : 31-diacetyl - uridine - 51 - benzylphosphite and halogenated to 21 : 31-diacetyluridine-51-benzylchlorophosphonate; (4) similarly to (3) there are prepared 21 : 31 - isopropylidene - adenosine - 51 - benzylphosphite and 51 - benzylchlorophosphonate; the latter is reacted with mono-silver riboflavin-51-phosphate (from the di-silver salt and the free acid) and the product hydrolysed to P-(riboflavin-51)-P1-(adenosine51) - dihydrogenpyrophosphate (purified via silver salt); this is identical with the natural flavin - adenine - dinucleotide (FAD). The process is applicable to any purine or pyrimidine nycleoside obtained by hydrolysing ribonucleic and deoxyribonucleic acids. Specifications 621,094 and 697,473 are referred to.