The development work toward the robust and efficient manufacturing process to vismodegib, the active pharmaceutical ingredient (API) in Erivedge, is described. The optimization of the four-stage manufacturing process was designed to produce the API with the required critical quality attributes: (1) the selective catalytic hydrogenation reduction of the nitro compound 3 to the corresponding aniline 4 while minimizing the formation of potential genotoxic (mutagenic) impurities; (2) the control of the polymorphic phase and multipoint specification for particle size distribution.

We describe the synthesis of (5'S)-5'-C-butylthymidine (5a), of the (5'S)-5'-C-butyl-and the (5'S)-5'-Cisopentyl derivatives 16a and 16b of 2'-deoxy-5-methylcytidine, as well as of the corresponding cyanoethyl phosphoramidites 9a, b and 14a, b, respectively. Starting from thymidin-5'-al 1, the alkyl chain at C(5') is introduced via Wittig chemistry to selectively yield the (Z)-olefin derivatives 3a and 3b (Scheme 2). The secondary OH function at C(5') is then introduced by epoxidation followed by regioselective reduction of the epoxy derivatives 4a and 4b with diisobutylaluminium hydride. In the latter step, a kinetic resolution of the diastereoisomer mixture 4a and 4b occurs, yielding the alkylated nucleoside 2a and 2b, respectively, with (5'S)-configuration in high diastereoisomer purity (de 94%). The corresponding 2'-deoxy-5-methylcytidine derivatives are obtained from the protected 5'-alkylated thymidine derivatives 7a and 7b via known base interconversion processes in excellent yields (Scheme 3). Application of the same strategy to the purine nucleoside 2'-deoxyadenine to obtain 5'-C-butyl-2'-deoxyadenosine 25 proved to be difficult due to the sensitivity of the purine base to hydride-based reducing agents (Scheme 4).

Dedicato a Duilio Arigoni per il suo 75O compleanno A series of oligonucleotides containing (5'S)-5'-C-butyl-and (5'S)-5'-C-isopentyl-substituted 2'-deoxyribonucleosides were designed, prepared, and characterized with the intention to explore alkyl-zipper formation between opposing alkyl chains across the minor groove of oligonucleotide duplexes as a means to modulate DNA-duplex stability. From four possible arrangements of the alkyl groups that differ in the density of packing of the alkyl chains across the minor groove, three (duplex types I ± III, Fig. 2) could experimentally be realized and their duplex-forming properties analyzed by UV-melting curves, CD spectroscopy, and isothermal titration calorimetry (ITC), as well as by molecular modeling. The results show that all arrangements of alkyl residues within the minor groove of DNA are thermally destabilizing by 1.5 ± 38/modification in T m . We found that, within the proposed duplexes with more loosely packed alkyl groups (type-III duplexes), accommodation of alkyl residues without extended distorsion of the helical parameters of B-DNA is possible but does not lead to higher thermodynamic stability. The more densely packed and more unevenly distributed arrangement (type-II duplexes) seems to suffer from ecliptic positioning of opposite alkyl groups, which might account for a systematic negative contribution to stability due to steric interactions. The decreased stability in the type-III duplexes described here may be due either to missing hydrophobic interactions of the alkyl groups (not bulky enough to make close contacts), or to an overcompensation of favorable alkyl-zipper formation presumably by loss of structured H 2 O in the minor groove.