On the antibiotic activity of oxazolomycin

Article abstract of DOI:10.1016/j.bmcl.2008.05.105

Structural analysis of oxazolomycin and simpler fragments containing a common 3-hydroxy-2,2-dimethylpropanamide moiety has indicated that a U-shaped conformation is preferred, in some cases stabilised by hydrogen bonding between the N-H and O-H residues, as shown by a combination of molecular modelling, NMR spectroscopic and single crystal X-ray analysis. A direct synthesis of this unit has been established via the opening of β-lactones by a range of amines, and their antibacterial activity been shown to vary with the hydrophobic character of the substituents.

Full text of DOI:10.1016/j.bmcl.2008.05.105

Bioorganic & Medicinal Chemistry Letters 18 (2008) 4081–4086
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
On the antibiotic activity of oxazolomycin
*
Claire L. Bagwell, Mark G. Moloney , Amber L. Thompson
Department of Chemistry, Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford OX1 3TA, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
Structural analysis of oxazolomycin and simpler fragments containing a common 3-hydroxy-2,2-dimeth-
ylpropanamide moiety has indicated that a U-shaped conformation is preferred, in some cases stabilised
by hydrogen bonding between the N–H and O–H residues, as shown by a combination of molecular mod-
elling, NMR spectroscopic and single crystal X-ray analysis. A direct synthesis of this unit has been estab-
lished via the opening of b-lactones by a range of amines, and their antibacterial activity been shown to
vary with the hydrophobic character of the substituents.
Received 22 April 2008
Revised 23 May 2008
Accepted 24 May 2008
Available online 14 June 2008
Keywords:
Oxazolomycin
Antibiotic
Ó 2008 Elsevier Ltd. All rights reserved.
Bioactivity
Conformation
The oxazolomycins1 1, the first originally isolated in 1985,2 and
the most recent, lajollamycin 2, isolated much later in 2005,3 are
structurally novel antibiotic and antiviral agents, whose bioactivity
has been proposed to arise from their protonophoric properties
and whose biosynthesis has been the recent focus of attention.4,5
Only one member, neooxazolomycin, has been successfully syn-
thesised,6,7 although a number of groups have established strate-
gies for the synthesis of core components, including the lactam,8–13
the middle component,14 and the left-hand portion.15–18 Related
compounds, with various structural elements common to the oxa-
zolomycins, such as inthomycin19–21 and clathrynamide,22 have
also been the focus of attention. It has been reported that the ob-
served antimicrobial properties of the oxazolomycins are a result
of their protonophoric activity,23,24 similar to the lipopeptaibols,
a family of membrane active antimicrobial peptides.25
Amongst a number of unusual structural features of this com-
pound, the central amide function is remarkable for the proximal
geminal dimethyl and b-hydroxy functions. Although it is clearly
not so hindered that amide bond formation is not possible, as the
two extant syntheses of neooxazolomycin testify,6,7 it seemed to
us that this gem-dimethyl amide motif was likely to enforce a U-
shaped structure on the molecule on the basis of the Thorpe–In-
gold effect,26 and that this might in turn be an important element
to the observed bioactivity of the oxazolomycins; such an arrange-
ment would be expected to give a polar lactam-lactone head group,
and a non-polar tail. We report here results which suggest that
oxazolomycin is in fact likely to adopt such a conformation, as do
suitably substituted but simpler gem-dimethyl amides, and that
the latter can exhibit antibacterial activity in their own right.
Molecular modeling27 of the truncated structure 3 of oxazolo-
mycin generated an energy minimised structure in which the gem-
inal dimethylamide portion induced a turn, likely to be stabilised
by a hydrogen bond as a result of the predicted close proximity
of the N–H and C-3 hydroxyl groups (2.07 Å) (Fig. 1). Of interest
was that in the modelling of oxazolomycin B 1b itself, the mini-
mum energy conformation (see Fig. 2) generated by AM1 semi-
empirical (SPARTAN) calculation gave a U-shaped preferred con-
formation with an NH–O distance of 4.07 Å, too long for effective
hydrogen bonding, but that this was indeed the preferred confor-
mation was suggested by modelling a more linear structure, which
was nearly 6 kcal/mol higher in energy and for which the NH. . .O
distance was 4.65 Å. Similarly, the modelling of inthomycin B 4, a
primary amide lacking the dienyl substituent of oxazolomycin,
indicated a structure which (Fig. 3) has an NH-O distance of
2.07 Å but which is clearly linear. A similar trimethyl substitution
pattern to that found in the oxazolomycins has been reported to
effectively control conformation in cyclic prodrugs,28 and the po-
tential influence of acyclic stereocontrol for the maintenance of
antibacterial bioactivity is illustrated by the importance of intra-
molecular hydrogen bonds in the non-peptidic antibacterial anti-
mycin A29 and of conformational effects in pediocin.30 On this
basis, a more detailed examination of the synthesis and structure
of the gem-dimethyl amide motif was warranted; desirable in
any synthesis was the capacity to readily modify the amide flank-
ing groups in order to explore their effect on antibacterial activity.
We found that the required gem-dimethyl amides were most
readily generated by reaction of the enolate of phenyl isobutyrate
5 with aldehydes according to the literature method31; when
* Corresponding author. Tel.: +44 1 865 275656; fax: +44 1865 285002.
E-mail address: mark.moloney@chem.ox.ac.uk (M.G. Moloney).
0960-894X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2008.05.105

4082
C. L. Bagwell et al. / Bioorg. Med. Chem. Lett. 18 (2008) 4081–4086
applied to benzaldehyde, the corresponding b-lactone 6 was gener-
ated in 75% yield (Scheme 1). This could be opened by treatment
with primary saturated and unsaturated amines, to give the amides
7a–e in good to excellent yield,32 although this reaction could be
sluggish, as might be expected of such a hindered lactone, requiring
extended reaction time at 40 °C to force the reaction to completion,
whilst avoiding the expected competing decarboxylation side reac-
tion which would occur at high temperature. That these structures
exist in a U-shaped conformation in solution was suggested by nOe
analysis of 7a, which showed enhancements of N–H, Me and
C(H)OH protons (Scheme 1), and in the case of 12b, single crystal
X-ray analysis (Fig. 4a and Tables 1 and 3)33 clearly indicated a hair-
pin structure, stabilised by an intramolecular hydrogen bond as a
result of the predicted close proximity of the N–H and C-8 hydroxyl
groups (2.29 Å), consistent with the in silico result. The sequence
was also applicable to ketones, as exemplified by the reaction of
cyclohexanone with phenyl isobutyrate 5 followed by ring opening
with allylamine, to give amide 9 in excellent overall yield. Variation
in the acyl side chain substitution pattern was also possible, as
shown by the reaction of aldehydes 10a–e giving amides 12a–e in
excellent overall yield (see Scheme 2). Although the aldehyde 10d
was easily prepared as shown in Scheme 3, attempted coupling of
bromide 11e with the same styrylboronate gave not the expected
b-lactone, but the alkene (E)-1-(2-methylprop-1-enyl)-2-styryl-
benzene, from Suzuki coupling followed by direct decarboxylation,
in 34% yield as a result of the high temperature which was used. In
Figure 2. Minimum energy conformation for oxazolomycin
ꢀ252.4 kcal/mol, NH. . .O distance 4.07 Å).
B 1b (energy =
but only in the presence of zinc chloride (2 equivalents); in the ab-
sence of zinc chloride, only the elimination products 15 and 16
were obtained in low yield, resulting from spontaneous decarboxyl-
ation of the b-lactone which was initially formed, along with unre-
acted starting material. It would appear that the zinc chloride acts
as a Lewis acid, promoting the initial aldol addition, but also pre-
venting the subsequent cyclisation by chelation across the b-
hydroxycarbonyl group. These esters could be easily converted to
amides 17 and 18 by aminolysis. Single crystal X-ray analysis of
the case of
a,b-unsaturated aldehydes (see Scheme 4), the aldol ad-
ducts 13 and 14 rather than the expected b-lactones were formed,
Figure 1. Minimum energy conformation for amide 3.

C. L. Bagwell et al. / Bioorg. Med. Chem. Lett. 18 (2008) 4081–4086
4083
Figure 3. Minimum energy conformation for inthomycin 4.
Scheme 1.
Scheme 2.
17 clearly indicated a linear structure, stabilised by an intermolec-
MIC values for oxazolomycins A–C 1a–c are in excess of 100 lg/
ular hydrogen bond (Fig. 4b and Table 1).33
ml,36 the most active fragments 7a, 12c and 12d are approximately
only 5 times lower in activity. The bioactivity of these compounds
broadly correlates with their hydrophobicity, as shown from their
LogP values; the exceptional compounds are bromophenyl deriva-
tive 7e and amide 18.
Bioassay against Staphylococcus aureus and Escherichia coli gave
the results indicated in Table 2.34 Derivative 12c showed the best
activity against S. aureus, although both 12d and 18 exhibited
weaker activity, with potency values relative to cephalosporin C
of some 5–8%; the minimum inhibitory concentration of the most
active compound 12c was found to be 4 mg/ml, making this com-
pound approximately 80-fold less active than KSM-2690, a mem-
ber of the oxazolomycin family reported to be active against
It is noteworthy that the common 3-hydroxy-2,2-dimethylpro-
panamide motif present in these compounds, and the parent oxa-
zolomycins, complies with the Lipinski ‘Rule of Five’37 and is a
versatile lead-like template suitable for library generation with at
least two points of chemical diversity. The value of such Lipinski-
compliant natural products with the required physicochemical
properties for lead structures for drug discovery has recently been
elaborated.38
S. aureus at 50 l
g/ml.35 Much higher levels of activity were found
against E. coli, and 12a, 12c, 12d and 18 in particular exhibited po-
tent activity at 4 mg/ml; their minimum inhibitory concentration
was found to be in the range 0.5–1 mg/ml. Since the reported

4084
C. L. Bagwell et al. / Bioorg. Med. Chem. Lett. 18 (2008) 4081–4086
Figure 4. Crystal structures of (a) compound 12b and (b) compound 17 showing the hydrogen bonding interactions detailed in Table 1. Thermal ellipsoids shown at 15%
probability level.
Table 1
Hydrogen bonds for compounds 12b and 17 (in Å and °; symmetry transformations used to generate equivalent atoms: #1 ꢀx + 1, y + 1/2, ꢀz + 2 #2 ꢀx + 1, y ꢀ 1/2, ꢀz + 2)
Compound
D–H. . .A
D(D–H)
D(H. . .A)
D(D. . .A)
<(DHA)
12b
17
N(3)–H(31). . .O(9)
N(16)–H(161). . .O(15)#1
O(1)–H(11). . .O(15)#2
0.89
0.90
0.86
2.29
2.27
1.90
2.851(2)
3.104(3)
2.739(3)
121
154
168
In conclusion, we have shown that the 3-hydroxy-2,2-dim-
ethylpropanamide motif present in the oxazolomycins is likely
to induce a turn in the preferred molecular conformation, and
that, appropriately substituted, it can exhibit antibacterial
activity. This natural product inspired motif is therefore of
interest, since it may provide a template for library generation
capable of ready optimisation against a number of bacterial
targets.
Scheme 3.
Table 2
Bioassay of compounds 4–9 against S. aureus and E. coli using the hole plate method
Compound
LogPa
Bioactivityb
S. aureus
E. coli
Zone size/mm
Relative potencyc
MICd
Zone size/mm
Relative potencyc
MICd (mg/ml)
7a
7b
7c
7d
7e
9
12a
12b
12c
12d
17
3.59
2.07
2.55
2.68
4.42
2.26
3.73
2.83
4.08
4.74
2.14
2.83
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
17
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
4
17
15
0.005
0.003
—
—
—
—
0.01
—
0.01
0.01
–
0.5
nd
—
—
—
—
1.0
—
0.5
0.5
—
Inactive
Inactive
Inactive
Inactive
22
Inactive
23
20
0.08
0.06
—
14
Inactive
14
nd
—
—
Inactive
28
18
0.05
0.03
1.0
a
LogP calculated using ChemBioDraw Ultra 11.0.
b
c
Hole plate bioassay at 4 mg/ml (7:3 DMSO/H2O).34
Expressed as zone size per mg/ml, relative to cephalosporin C standard.
Minimum inhibitory concentration estimated by serial dilution until no inhibition zone is observed; nd, not determined.
d

C. L. Bagwell et al. / Bioorg. Med. Chem. Lett. 18 (2008) 4081–4086
4085
Scheme 4.
6. Onyango, E. O.; Tsurumoto, J.; Imai, N.; Takahashi, K.; Ishihara, J.; Hatakeyama,
S. Angew. Chem., Int. Ed. 2007, 46, 6703.
Table 3
Crystals structure data for compounds 12b and 17
7. Kende, A. S.; Kawamura, K.; DeVita, R. J. J. Am. Chem. Soc. 1990, 112, 4070.
8. Bennett, N. J.; Prodger, J. C.; Pattenden, G. Tetrahedron 2007, 63, 6216.
9. Donohoe, T. J.; Chiu, J. Y. K.; Thomas, R. E. Org. Lett. 2007, 9, 421.
10. Mohapatra, D. K.; Mondal, D.; Gonnade, R. G.; Chorghade, M. S.; Gurjar, M. K.
Tetrahedron Lett. 2006, 47, 6031.
Compound
12b
17
Chemical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
C
15H21NO2
C13H17NO2
219.28
150
0.71073
Orthorhombic
P 21
6.0960(2)
8.2767(3)
11.9649(5)
90
102.1584(12)
90
590.14(4)
2
1.234
0.083
236
247.34
150
0.71073
Monoclinic
P 21/c
13.9977(3)
7.9134(2)
12.5315(5)
90
91.3997(12)
90
1387.69(7)
4
1.184
0.078
536
11. Papillon, J. P. N.; Taylor, R. J. K. Org. Lett. 2000, 2, 1987.
12. Andrews, M. D.; Brewster, A. G.; Crapnell, K. M.; Ibbett, A. J.; Jones, T.; Moloney,
M. G.; Prout, K.; Watkin, D. J. Chem. Soc., Perkin Trans. 1 1998, 223.
13. Andrews, M. D.; Brewster, A. G.; Moloney, M. G. Synlett 1996, 612.
14. Wang, Z.; Moloney, M. G. Tetrahedron Lett. 2002, 43, 9629.
15. Marino, J. P.; Nguyen, H. N. Tetrahedron Lett. 2003, 44, 7395.
16. Bulger, P. G.; Moloney, M. G.; Trippier, P. C. Org. Biomol. Chem. 2003, 1, 3726.
17. Bulger, P. G.; Moloney, M. G.; Trippier, P. C. Synlett 2002, 1871.
18. Addie, M. S.; Taylor, R. J. K. J. Chem. Soc., Perkin Trans. 1 2000, 527.
19. Webb, M. R.; Donald, C.; Taylor, R. J. K. Tetrahedron Lett. 2006, 47, 549.
20. Whiting, A.; Henaff, N. Tetrahedron 2000, 56, 5193.
b (Å)
c (Å)
a
(°)
b (°)
(°)
c
Cell volume (Å3)
Z
21. Whiting, A.; Henaff, N. Org. Lett. 1999, 1, 1137.
22. Ojika, M.; Itou, Y.; Sakagami, Y. Biosci. Biotechnol. Biochem. 2003, 67, 1568.
23. Grigorjev, P. A.; Schlegel, R.; Grafe, U. Pharmazie 1992, 47, 707.
24. Tonew, E.; Tonew, M.; Grafe, U.; Zopel, P. Acta Virol. 1992, 36, 166.
25. Tonioloa, C.; Crismaa, M.; Formaggioa, F.; Peggiona, C.; Epand, R. F.; Epand, R.
M. Cell. Mol. Life Sci. 2001, 58, 1179.
Calculated density (mg/m3)
Absorption coefficient (mmꢀ1
F0 0 0
)
Crystal size (mm)
Reflections measured
Unique reflections
Rint
Observed reflections (I > 2
Parameters refined
Goodness of fit
0.20 ꢁ 0.15 ꢁ 0.07 0.18 ꢁ 0.18 ꢁ 0.18
17901
3152
0.058
2368
163
10880
1435
0.045
1356
145
0.9995
0.0348
0.0859
ꢀ0.17, 0.16
26. Beesley, R. M.; Ingold, C. K.; Thorpe, J. F. J. Chem. Soc., Trans. 1915, 107, 1080.
27. The preferred lowest energy conformation was calculated in the case of 3 and 4
AM1 semi-empirical calculations, and in the case of oxazolomycin 1b by using
*
the Hartree–Fock method (6-31G basis set) after the initial starting
r
(I))
conformation was obtained from a sequential conformational search using
CAChe Version 4.4.1 software. Kong, J.; White, C. A.; Krylov, A. I.; Sherrill, C. D.;
Adamson, R. D.; Furlani, T. R.; Lee, M. S.; Lee, A. M.; Gwaltney, S. R.; Adams, T.
R.; Ochsenfeld, C.; Gilbert, A. T. B.; Kedziora, G. S.; Rassolov, V. A.; Maurice, D.
R.; Nair, N.; Shao, Y.; Besley, N. A.; Maslen, P. E.; Dombroski, J. P.; Daschel, H.;
Zhang, W.; Korambath, P. P.; Baker, J.; Byrd, E. F. C.; Van Voorhis, T.; Oumi, M.;
Hirata, S.; Hsu, C.-P.; Ishikawa, N.; Florian, J.; Warshel, A.; Johnson, B. G.; Gill, P.
M. W.; Head-Gordon, M.; Pople, J. A. J. Comput. Chem. 2000, 21, 1532.
28. Wang, B.; Gangwar, S.; Pauletti, G. M.; Siahaan, T. J.; Borchardt, R. T. J. Org.
Chem. 1997, 62, 1363–1367.
0.9845
0.0488
0.1268
ꢀ0.29, 0.25
R(I > 2
wR(I > 2
Residual electron density (min,max)
(eÅꢀ3
r
(I))
r
(I))
)
29. Miyoshi, H.; Tokutake, N.; Imaeda, Y.; Akagi, T.; Iwamura, H. Biochim. Biophys.
Acta 1995, 1229, 149–154.
Supplementary data
30. Gaussier, H.; Lavoie, M.; Subiradea, M. Int. J. Biol. Macromol. 2003, 32, 1–9.
31. Wedler, C.; Kunath, A.; Schick, H. J. Org. Chem. 1995, 60, 758.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmcl.2008.05.105.
32. Representative procedure for the ring opening of b-lactones with amine
nucleophiles: ( )-N-Allyl-3-hydroxy-2,2-dimethyl-3-phenylpropanamide 7c. A
solution of 6 (40 mg, 0.23 mmol), dry Et3N (23 mg, 0.25 mmol) and allylamine
(66 mg, 1.16 mmol) in dry DCM (1 ml) in a flask fitted with a reflux condenser
was stirred at 40 °C for 24 h. The solvent was removed in vacuo and the
remaining residue loaded onto a flash chromatography column of silica gel.
Elution with 7:3 petrol/EtOAc furnished the desired product 7c (54 mg, 100%)
References and notes
1. Moloney, M. G.; Trippier, P. C.; Yaqoob, M.; Wang, Z. Curr. Drug Discov. Technol.
2004, 1, 181.
2. Mori, T.; Takahashi, K.; Kashiwabara, M.; Uemura, D.; Katayama, C.; Iwadare, S.;
Shizuri, Y.; Mitomo, R.; Nakano, F.; Matsuzaki, A. Tetrahedron Lett. 1985, 26,
1073.
3. Manam, R. R.; Teisan, S.; White, D. J.; Nicholson, B.; Grodberg, J.; Neuteboom, S.
T. C.; Lam, K. S.; Mosca, D. A.; Lloyd, G. K.; Potts, B. C. M. J. Nat. Prod. 2005, 68,
240.
4. Dorrestein, P. C.; Van Lanen, S. G.; Li, W. L.; Zhao, C. H.; Deng, Z. X.; Shen, B.;
Kelleher, N. L. J. Am. Chem. Soc. 2006, 128, 10386.
as a thick, colourless oil: Rf 0.18 (7:3 petrol/EtOAc);
t
max(film)/cmꢀ1 3345,
2978, 1642, 1538, 1177 and 1048; dH (200 MHz; CDCl3; Me4Si) 1.06 (3H, s, 2-
CH3), 1.20 ð3H; s; 2 ꢀ CH03Þ, 3.83 (2H, dt, J 5.6 and 1.4, 10-CH2), 4.60 (1H, s, H-3),
4.66 (1 H, br s, OH), 5.07–5.15 (2H, m, 30-CH2), 5.68–5.85 (1 H, m, H-20), 6.28
(1H, br s, NH) and 7.22–7.34 (5 H, m, 5ꢁ ArCH); dC (100.6 MHz; CDCl3; Me4Si)
20.6 (2-CH3), 24.4 ð2 ꢀ CH0 Þ, 41.8 (C-10), 46.2 (C-2), 79.9 (C-3), 116.3 (C-30),
127.6 (ortho- or meta-CH),3127.7 (para-CH), 127.8 (ortho- or meta-CH), 133.9
(C-20), 140.8 (ipso-C) and 177.6 (C-1); m/z (ESI+) 291 ([M+CH3CN+NH4]+, 36%)
and 256 (16, [M+Na]+); HRMS (ESI+): found 256.1296, C14H19NNaO2 requires
256.1308. ( )-N-Allyl-3-hydroxy-2,2-dimethyl-7-phenylheptanamide 12c. Thick,
5. Zhao, C. H.; Ju, J. H.; Christenson, S. D.; Smith, W. C.; Song, D. F.; Zhou, X. F.;
Shen, B.; Deng, Z. X. J. Bacteriol. 2006, 188, 4142.

4086
colourless oil, 89%: Rf 0.14 (7:3 petrol/EtOAc);
C. L. Bagwell et al. / Bioorg. Med. Chem. Lett. 18 (2008) 4081–4086
t
max(film)/cmꢀ1 3338, 3085,
Crystallographic Data Centre as supplementary publication numbers CCDC
687802 and 687803. Copies of the data can be obtained, free of charge, on
application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [fax: +44
(0)1223 336033 or e-mail: deposit@ccdc.cam.ac.uk.
3026, 2934, 2859, 1640, 1537, 1454, 1259, 1181, 1079 and 990; dH (400 MHz;
CDCl3; Me4Si) 1.14 (3H, s, 2-CH3), 1.25 ð3H; s; 2 ꢀ CH0 Þ, 1.26–1.40, 1.51–1.54,
1.61–1.69 (6H, series of m, 4-, 5- and 6-CH2), 2.62 (2H,3m, 7-CH2), 3.46 (1H, dd, J
9.5 and 6.3, H-3), 3.66 (1H, br s, OH), 3.87 (2H, m, 10-CH2), 5.13 (1H, d, J 10.2, H-
30), 5.19 (1H, d, J 17.1, H0-30), 5.84 (1H, ddt, J 17.1, 10.2 and 5.5, H-20), 6.47 (1H,
br s, NH) and 7.16–7.30 (5H, m, 5ꢁ ArCH); dC (100.6 MHz; CDCl3; Me4Si) 21.1
(2-CH3), 24.5 ð2 ꢀ CH03Þ, 26.4, 31.5, 31.7 (C-4, -5 and -6), 36.0 (C-7), 41.6 (C-10),
45.9 (C-2), 77.7 (C-3), 116.1 (C-30), 125.6 (para-CH), 128.3, 128.4 (ortho- and
meta-CH), 134.3 (C-20), 142.6 (ipso-C) and 177.8 (C-1); m/z (ESI+) 312 ([M+Na]+,
23%), 290 (45,[M+H]+) and 103 (55); HRMS (ESI+): found 312.1934,
34. Bioassay of penicillin products.42–44 Microbiological assays were performed by
the hole-plate method with the test organism Staphylococcus aureus N.C.T.C.
6571 or E. coli X580. Solutions (100 ll) of the compounds to be tested (4 mg/
ml) were loaded into wells in bioassay plates, and incubated overnight at 37 °C.
The diameters of the resultant inhibition zones were measured, and relative
potency estimated by reference to standards prepared with Cephalosporin C.
Minimum inhibitory concentrations were estimated by serial dilution until no
inhibition zones were obtained after bioassay.
C
18H27NNaO2 requires 312.1934.
33. Crystals of 12b and 17 were grown by slow diffusion. Single crystal X-ray
diffraction data were collected using graphite monochromated Mo
radiation (k = 0.71073 Å) on an Enraf-Nonius KappaCCD diffractometer. The
diffractometer was equipped with Cryostream N2 open-flow cooling
device,39 and the data were collected at 150(2) K. Series of
-scans were
performed in such way as to cover sphere of data to maximum
35. Otani, T.; Yoshida, K.-I.; Kubota, H.; Kawai, S.; Ito, S.; Hori, H.; Ishiyama, T.; Oki,
T. J. Antibiot. 2000, 53, 1397.
K
a
36. Kanzaki, H.; Wada, K.; Nitoda, T.; Kawazu, K. Biosci. Biotechnol. Biochem. 1998,
62, 438.
a
x
a
37. Lipinski, C. A.; Lombardo, F.; Dominy, B. W.; Feeney, P. J. Adv. Drug Deliv. Rev.
2001, 46, 3.
a
a
resolution of 0.77 Å. Cell parameters and intensity data were processed
using the DENZO-SMN package40 and the structures were solved by direct
methods and refined by full-matrix least squares on F2 using the CRYSTALS
suite.41 Intensities were corrected for absorption effects by the multi-scan
method, based on multiple scans of identical and Laue equivalent
reflections. All non-hydrogen atoms were refined with anisotropic
displacement parameters. Hydrogen atoms were initially positioned
38. Quinn, R. J.; Carroll, A. R.; Pham, N. B.; P.Baron; Palframan, M. E.; L.Suraweera;
Pierens, G. K.; Muresan, S. J. Nat. Prod. 2008, 71, 464.
39. Cosier, J.; Glazer, A. M. J. Appl. Cryst. 1986, 19, 105.
40. Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276, 307.
41. Betteridge, P. W.; Carruthers, J. R.; Cooper, R. I.; Prout, K.; Watkin, D. J. J. Appl.
Cryst. 2003, 36, 1487.
42. Smith, B.; Warren, S. C.; Newton, G. G. F.; Abraham, E. P. Biochem. J. 1967, 103,
877.
geometrically and optimised using restraints, then refined using
a riding
model. Crystal data and structure refinement parameters are included in
Table 3. Crystallographic data (excluding structure factors) for the
structures in this letter have been deposited with the Cambridge
43. Baldwin, J. E.; Coates, J. B.; Halpern, J.; Moloney, M. G.; Pratt, A. J. Biochem. J.
1989, 261, 197.
44. Baldwin, J. E.; Pratt, A. J.; Moloney, M. G. Tetrahedron 1987, 43, 2565.