X-ray structures of five variably tert-butoxycarbonyl-substituted adenines and their liquid and solid state NMR investigations

Two tautomeric polymorphs of 2,6-dichloropurine

“…In (I), the N Csp 2 bond corresponds to N7-C8 [1.310 (5) Å ] and N17-C18 [1.307 (5) Å ] for molecules A and B, respectively, while in (II) it is N9-C8 [1.327 (3) Å ]. These N Csp 2 bond lengths are comparable with those in related structures with 9H- (Mahapatra et al, 2008;Trá vníček & Rosenker, 2006;Soriano-Garcia & Parthasarathy, 1977) and 7H-tautomers (Bo et al, 2006;Ikonen et al, 2009;Watson et al, 1965). The -N(H) tautomeric position is also evident from the greater ring angle at the site where the H atom is attached, namely N9 [C4-N9-C8 = 105.9 (3) ] and N19 [C14-N19-C18 = 105.6 (3) ] for (I), and N7 [C5-N7-C8 = 105.9 (2) ] for (II), compared with the ring angle involving the -N C-bond [for (I), C5-N7-C8 = 103.6 (3) and C15-N17-C18 = 103.8 (3) ; for (II), C4-N9-C8 = 103.6 (2) ].…”

NMR Spectroscopic Study of Tautomerism in Solution and in the Solid State

“…The N-OH tautomer is the only one present in the solid state [104]. detected [108]. Presence of the still missing C(6)=NH imino form in nucleotides was confirmed by double quantum filtered-correlation spectroscopy (DQF-COSY) NMR experiments at low temperature [109].…”

Geometric changes around an N atom due to a urethane-type bis(tert-butoxycarbonyl) substituent

“…The tert-butoxycarbonyl (Boc) and bis(tert-butoxycarbonyl) (bis-Boc) groups are frequently used to protect amino groups. While Boc-protected organic structures are fairly well represented (452 hits) in the Cambridge Structural Database (CSD, Version 5.33; Allen, 2002), to the best of our knowledge only nine organic structures with bis-Boc protection on the N atom have been deposited to date, and the structures of only two sets of compounds with Boc and bis-Boc protection are available in the CSD [CSD refcodes MUTTOK and MUTTUQ (Macleod et al, 2003), and XUDQUJ and XUDQOD (Ikonen et al, 2009)]. During the synthesis of some novel nonproteinaceous amino acids, we obtained two derivatives of aspartic acid, and their structures form a third pair of this type.…”

“…In (II), carbonyl atom O5 is synperiplanar to atom C3 and carbonyl atom O7 is antiperiplanar to atom C3. In the other two bis-Boc compounds, the carbonyl O atoms are oriented in the same direction, both antiperiplanar to the C-N bond, but these structures are much less crowded (Macleod et al, 2003;Ikonen et al, 2009). Four very weak intramolecular hydrogenbond contacts of C-HÁ Á ÁO type (C9-H9AÁ Á ÁO5, C11-H11CÁ Á ÁO5, C15-H15CÁ Á ÁO7 and C16-H16AÁ Á ÁO7; Table 4) stabilize the conformation of both Boc groups in (II) ( Fig.…”