Calystegines structures

Figure 4 Possible contributions to the equilibrium between bicyclic aminoketal rings and monocyclic aminoheptanones and tautomerisations to calystegine structure variation.

Preparation of polyhydroxylated 6-oxanortropane glycomimetics (e.g. 32), structurally related to the glycosidase inhibitor family of the calystegines, was reported. The synthetic strategy involves the furanose/piperidine... 

Goldmann, A., B. Message, D. Tepfer, R. J. Molyneux, O. Duclos, F. D. Boyer, and A. D. Elbein. Biological activities of the nortropane alkaloid, calystegine B2, and analogs structure-function relationships. J. Nat. Prod. 59 1137-1142. 

Callipeltoside A, via Alder-ene reactions, 10, 593 Calorimetry, in thermochemistry, 1, 610-611 Calystegine B2, via ring-closing diene metathesis, 11, 210-211 Cambridge Structural Database, in structure determination,... 

Fig. 14.10 Structures and chemical shift assignments of calystegins monitored in root cultures of Calystegia sepium [79]. chemical shifts were reported relative to potassium N-nitrate. Chemical shifts in this figure have been referenced to liquid NH3 using 376.5 ppm, the chemical shift of sodium N-nitrate in water as the conversion factor.

Nakajima K, Yamashita A, Akama H, Nakatsu T, Kato H, Hashimoto T, Oda J, Yamada Y. Crystal structures of two tropinone reductases different reaction stereospecificities in the same protein fold. Proc. Natl. Acad. Sci. 1998 95 4876-4881. Drager B. Chemistry and biology of calystegines. Nat. Prod. Rep. 2004 21 211-223. 

Calystegines and Related Afortropane Alkaloids 2. ISOLATION AND STRUCTURAL ELUCIDATION. 

All of the calystegines isolated to date have been obtained as amorphous white solids and melting points have therefore not been reported. Structures have been determined by spectroscopic methods, in particular H and 1SC NMR spectroscopy and high-resolution mass spectrometry. Additional confirmatory evidence has been obtained from analysis of the alkaloids as trimethylsilyl ether derivatives by gas chromatography - mass spectrometry (Section 4.4). In certain cases the structures and absolute configurations have been confirmed by synthesis (Section 6). 

The structure of a 3-0- p -D-glucopyranoside of calystegine B, was determined by the use of 2D NMR spectroscopy [32], The linkage site was established by a correlation peak in the HMBC spectrum between the anomeric proton and the aglycone C(3) carbon. A downfield shift fix the C(3) resonance and upfield shifts for the C(2) and C(4) resonances in the 13C NMR spectrum, relative to the aglycone, provided additional confirmation for the structure. 

It should be noted that this alkaloid was originally named nortropanoline by Asano and coworkers but its structural identity to the previously discovered calystegine B2 [10] was... 

The NMR data accumulated fix the calystegines identified to date is quite comprehensive and should enable novel structures in the class to be elucidated fairly easily by comparison with established structures. The H and I3C NMR chemical shifts and coupling constants determined for the above nine alkaloids are tabulated in Table 1 and Table 2, respectively. 

The specific rotations for the synthetic calystegine A, enantiomer hydrochlorides were +12.4° and -12.2s, respectively. Since the rotation of the hydrochloride salt of calystegine A3 has not been reported the synthesis does not unequivocally define the absolute configuration of the natural product, but the assumption was made that the alkaloid has the same absolute configuration as calystegine B i.e. IR,2S,3R,5R as shown in structure (14). 

These initial results were subsequently confirmed with pure calystegines Bt and B2 [23,24], and extended to other members of the series as they were discovered [25-27], The ICM and X values have been summarized by Asano et al. [26,27], Comparison of the extent of inhibitory activity with variation in structure or stereochemistry allows certain broad conclusions to be drawn, as follows ... 

Calystegins A3, Bi and B2 (257a-c) were isolated from Calystegia sepium. These alkaloids were also present in Convolvus arvenis and Atropa belladonna, and they were found to be catabolized by Rhizobium meliloti strain 41 [584], The structures of 257a-c were determined with HRMS, and H and NMR, and were confirmed by the synthesis and NMR analysis of model compounds [585], C-Putrescine served as a biosynthetic precursor for the calystegins [586],... 

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