tert-Butyl (2R,4aR,5aR,11aS,12R,12aR)-8-[bis(tert-butoxycarbonyl)amino]-12-hydroxy-2-methoxy-2,10-dioxo-4,4a,5a,6,9,10,11,11a,12,12a-decahydro-2H-1,3,5-trioxa-6,7,9,11-tetraaza-2λ5-phosphatetracene-6-carboxylate methanol monosolvate monohydrate

The title compound, C26H40N5O13P·CH3OH·H2O, crystallizes with one water and one methanol molecule providing important crystal-binding interactions. The compound has the unusual feature of having two butoxycarbonyl groups bound to one N atom. The conventional attractive hydrogen bonds involving hydroxy, amine and water donors include bifurcations at both donors and acceptors with novel R 1 2(6) and R 2 1(6) motifs. These are supplemented by C—H⋯O interactions between adjacent molecules forming chain and R 2 2(10) ring motifs.

The title compound, C 26 H 40 N 5 O 13 PÁCH 3 OHÁH 2 O, crystallizes with one water and one methanol molecule providing important crystal-binding interactions. The compound has the unusual feature of having two butoxycarbonyl groups bound to one N atom. The conventional attractive hydrogen bonds involving hydroxy, amine and water donors include bifurcations at both donors and acceptors with novel R 1 2 (6) and R 2 1 (6) motifs. These are supplemented by C-HÁ Á ÁO interactions between adjacent molecules forming chain and R 2 2 (10) ring motifs.

Comment
The title compound is an intermediate required for the synthesis of cyclic pyranopterin monophosphate, a molecule whose absence in humans leads to a rare metabolic disorder known as molybdenum cofactor deficiency type A (Veldman et al., 2010).
The title compound crystallizes with one independent C 26 H 40 N 5 O 13 P molecule in the asymmetric unit with one water and one methanol molecule of crystallization (Fig. 1). This and related compounds that were prepared are prone to form merohedrally twinned crystals; this non-twinned structure is the only one successfully solved and refined to date. The absolute configuration was determined using the oxygen anomalous dispersion effect, with the Hooft y parameter value calculated as -0.012 (13) (Spek, 2009). This confirms the expected configurations at C4a (R), C5a (R), C11a (S), C12 (R) and C12a (R).
There are only three closely related structures in the Cambridge Structural Database, namely GODXEC (Low et al., 1999), PUVCIS (Low et al., 1998) and ZENSAM (Low et al., 1995) with none of these involving a fourth fused ring as found here (ring 1, atoms C4a, C12a, O1, P2, O3 & C4). A common feature of all the structures is the buckling of the fused rings progressively away from the near planar ring 4 (C6a, N7, C8, N9, C10 & C10a; see Fig. 1). A comparison of the ring parameters, and their conformational forms (Cremer & Pople, 1975) is given in Table 2 (Ring parameters) with rings 2 & 3 consisting of atoms C5a, C11a, C12, C12a, C4a, O5 and N6, C6a, C10a, N11, C11a, C5a respectively. The similarity of the dihedral angles between the planes for ZENSAM (with the same ring absolute configuration) and PUVCIS (with the inverted configuration) implies that addition of the fourth "capping" ring 1 in the stable chair conformation has not required significant conformational changes to the other rings (see Table 3: Angles between ring planes).
The binding of two BOC groups on nitrogen N8 was slightly unexpected, with the second group expected to bind to the ring nitrogen N9. Indeed, a CSD search (Version 5.33, with Feb. 2012 update) indicates that this occurrence has been reported only 19 times whereas structures with BOC single binding are numbered in the multiple 1000's.
The crystal packing consists of a set of conventional N-H···O(water) and O-H···O(methanol, P, water) hydrogen bonds (see Table 1) which include bifurcations at both donors and acceptors with novel R 2 1 (6) and R 1 2 (6) motifs. These are supplemented by C-H···O interactions between adjacent molecules forming chain and R 2 2 (10) ring motifs (Bernstein et al., 1995).

Experimental
The details of the synthesis of the title compound will be published elsewhere in due course. The title compound was dissolved in methanol at ambient temperature and diethyl ether added. After 2 h the crystals were filtered off and washed with a little diethyl ether and dried at 15 Torr. The title compound was also crystallized from hot ethanol or hot ethanol and heptane mixtures followed by cooling to ambient temperature but the crystals produced in this way were twinned or were only weakly diffracting.