Synthesis of methyl sulfomycinate, sulfomycinic amide and sulfomycinine, degradation products of the sulfomycin thiopeptide antibiotics

Article abstract of DOI:10.1016/j.tet.2005.09.134

The convergent synthesis of methyl sulfomycinate and sulfomycinic amide, two acidic methanolysis products of the sulfomycin thiopeptide antibiotics, is achieved starting from diethoxyacetonitrile. Further confirmation of structure is obtained by heating m

Full text of DOI:10.1016/j.tet.2005.09.134

Tetrahedron 62 (2006) 66–72
Synthesis of methyl sulfomycinate, sulfomycinic amide and
sulfomycinine, degradation products of the sulfomycin
thiopeptide antibiotics
*
Mark C. Bagley and Christian Glover
School of Chemistry, Main Building, Cardiff University, Park Place, Cardiff CF10 3AT, UK
Received 11 August 2005; revised 12 September 2005; accepted 29 September 2005
Available online 28 October 2005
Abstract—The convergent synthesis of methyl sulfomycinate and sulfomycinic amide, two acidic methanolysis products of the sulfomycin
thiopeptide antibiotics, is achieved starting from diethoxyacetonitrile. Further confirmation of structure is obtained by heating methyl
sulfomycinate at 110 8C in hydrochloric acid to give (G)-sulfomycinine hydrochloride, the acid hydrolysate of sulfomycin I.
q 2005 Elsevier Ltd. All rights reserved.
1. Introduction
The thiopeptide antibiotics are a class of biologically active
natural products comprising 29 different families and at
least 76 structurally distinct sulfur-containing cyclic peptide
secondary metabolites isolated from the mycelial cake of
actinomycetes. Their biological properties have attracted
attention from a broad consortia of scientists and include
features as diverse as the inhibition of bacterial protein
synthesis, tipA promotion, renin inhibition and anti-malarial
activity.1 Since the first isolation of these natural products in
1948,2 structure elucidation of metabolites such as
micrococcin P1 (1) by NMR3 and the stunningly complex
thiostrepton (2) by X-ray crystallography (Fig. 1)4 has been
supported by synthetic studies. The laboratory preparation
of promothiocin A (3)5,6 and amythiamicin D (4)7 (Fig. 2)
served to verify the constitution and stereochemistry of
these thiopeptide families and recently the groundbreaking
synthesis of thiostrepton (2) was reported,8,9 demonstrating
that the synthesis of any members of this antibiotic class is
potentially within reach.
The sulfomycins (5) (Scheme 1) are one class of thiopeptide
antibiotics isolated from Streptomyces viridochromogenes
subsp. sulfomycini ATCC 29776 and MCRL-0368 with
strong inhibitory activity against Gram-positive bacteria.10
1
Chemical degradation studies,11,12 in combination with H
and 13C NMR spectroscopic and FAB mass spectrometric
Keywords: Sulfomycin; Thiopeptide antibiotics; Chemical degradation;
Thiazoles.
*
Corresponding author. Tel.: C44 29 2087 4029; fax: C44 29 2087 4030;
e-mail: bagleymc@cf.ac.uk
Figure 1. Micrococcin and thiostrepton thiopeptide antibiotics.
0040–4020/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2005.09.134

M. C. Bagley, C. Glover / Tetrahedron 62 (2006) 66–72
67
Acidic methanolysis of sulfomycin using Amberlyst 15
ion-exchange resin gave dimethyl sulfomycinamate (8),
sulfomycinic amide (9), and methyl sulfomycinate (10), the
latter of which was transformed to 7 in order to provide
corroborating data on structure (Scheme 1). Our synthesis of
dimethyl sulfomycinamate (8),17,18 by Bohlmann-Rahtz
reaction of an oxazolylenamine, further verified the identity
of this acidic methanolysis product to complement the
findings of Kelly,19 but the structures of degradation
products 9 and 10, which were proposed on the basis of
1
IR, UV, H NMR spectroscopic and MS data for 10,11 are
unconfirmed. In order to validate a route toward the
sulfomycins, and as part of our interest in the total
synthesis20,21 and stereochemistry of thiopeptide anti-
biotics,22 we set out to address this shortfall and establish
a convergent synthesis of methyl sulfomycinate (10).
2. Results and discussion
Methyl sulfomycinate (10) is a modified tripeptide
consisting of two fragments: an oxazole-containing
dipeptide 20 related to a known (K)-muscoride A building
block,23 and a 2-formylthiazole-4-carboxylate residue 15
that is also a component of the antibiotic althiomycin,24
present as its dimethyl acetal. Our convergent strategy
assembled each heterocyclic component in turn and then
coupled them together with subsequent dehydration to
elaborate the aminopropenyl unit of 10. Starting with
diethoxyacetonitrile (11), treatment with ammonium sulfide
in methanol at room temperature according to our recently
reported procedure gave thioamide 12 in excellent yield.25
Thiazole 13 was prepared by reaction with ethyl bromo-
pyruvate in ethanol under Hantzsch conditions. Trans-
acetalization under acidic conditions with p-toluenesulfonic
acid (TsOH) in methanol gave dimethyl acetal 14, which
Figure 2. Promothiocin and amythiamicin thiopeptide antibiotics.
data,13,14 elucidated their structure which contains an
oxazole–thiazole–pyridine series d domain but differs
between factors in the identity of one alkenyl substituent
(R) located on the cyclic peptide backbone. In these
degradation experiments, the acid hydrolysis of sulfomycin
I in concentrated hydrochloric acid at 110 8C gave
berninamycinic acid (6) and sulfomycinine (7) hydro-
chloride, both of which have been identified by X-ray
crystallographic methods and chemical synthesis.15,16
Scheme 1. Structure and chemical degradation of the sulfomycins.

68
M. C. Bagley, C. Glover / Tetrahedron 62 (2006) 66–72
was saponified using lithium hydroxide in methanol–water
either directly or after isolation to give thiazole-4-
carboxylic acid 15 in reasonable overall yield (Scheme 2).
Fluor)28 and oxidized to the oxazole 19 with CBrCl3–
DBU.29 Hydrogenolysis of the benzyloxycarbonyl (Cbz)
protecting group over Pd–C in methanol gave amine 20
which was coupled with thiazole-acid 15 using pyBOP to
give tripeptide 21 (Scheme 4). Finally protodesilylation by
treatment with TBAF in THF gave alcohol 22, which was
dehydrated via the corresponding methanesulfonate deriva-
tive to give methyl sulfomycinate (10). The physical and
spectroscopic properties of the synthetic material [mp 122–
123 8C; UV (MeOH)/nm lmax 246 (log 3 4.40)] were in very
good agreement with literature data on the degradation
product [lit.11 mp 124–124.5 8C; lit.11 UV (MeOH)/nm lmax
247 (log 3 4.38)] confirming the outcome of Abe’s
methanolysis studies11 and providing a viable route to this
region of the sulfomycin cyclic peptides.
Scheme 2. Synthesis of thiazole 15. Reagents and conditions: (a) (NH4)2S,
MeOH, RT, 18 h (100%); (b) ethyl bromopyruvate, EtOH, reflux, 1 h
(100%); (c) TsOH, MeOH, reflux, 6 h (66%); (d) LiOH, MeOH–H2O, RT,
18 h (64%); (e) TsOH, MeOH, reflux, 6 h; LiOH, MeOH–H2O, 48 h (54%).
Further confirmation of structure was obtained by carrying
out both the known ammonolysis and hydrolysis of 10, in
methanolic ammonia at room temperature for the former or
in hydrochloric acid at 110 8C for the latter, to obtain
sulfomycinic amide (9) and sulfomycinine (7) hydro-
chloride, respectively, with physical properties that
corroborated known data.16 This convergent synthesis thus
confirms both the structure of methyl sulfomycinate (10)
and the outcome of its chemical degradation, as well as
providing a method for the preparation of this fragment
applicable to the total synthesis of the sulfomycin
thiopeptide antibiotics.
3. Experimental
3.1. General
Scheme 3. Synthesis of oxazole 20. Reagents and conditions:
(a) TBDMSCl, imidazole, DMAP, DMF, RT, 36 h (100%); (b) LiOH,
MeOH–H2O, RT, 18 h (96%); (c) HCl$H-Thr-OMe, pyBOP, Et3N,
CH2Cl2, 0 8C–RT, 18 h (83%); (d) Deoxo-Fluor, CH2Cl2, K20 8C, 18 h
(65%); (e) CBrCl3, DBU, CH2Cl2, K20 8C, 18 h (52%); (dCe) without
isolation of pure 18 (52%); (f) H2, Pd–C, MeOH, RT, 3 h (93%).
Commercially available reagents were used without further
purification; solvents were dried by standard procedures.
Light petroleum refers to the fraction with bp 40–60 8C.
Flash chromatography was carried out using Merck
Kieselgel 60 H silica or Matrex silica 60. Analytical thin
layer chromatography was carried out using aluminium-
backed plates coated with Merck Kieselgel 60 GF254 that
were visualised under UV light (at 254 and/or 360 nm).
Melting points (mp) were determined on a Kofler hot stage
apparatus and are uncorrected. Infra-red (IR) spectra were
The other component, oxazole 20, was prepared according
to a modified method of Pattenden23 from an O-silyl ether
derivative of threonine 16 (Scheme 3).26,27 Peptide coupling
using benzotriazol-1-yloxytripyrrolidinophosphonium
hexafluorophosphate (pyBOP) in dichloromethane gave
dipeptide 17 which was cyclized to oxazoline 18 with
[bis(2-methoxyethyl)amino]sulfur trifluoride (Deoxo-
Scheme 4. Synthesis of methyl sulfomycinate (10). Reagents and conditions (a) pyBOP, CH2Cl2, 0 8C–RT, 18 h (88%); (b) TBAF, THF, 0 8C–RT, 5 h (77%);
(c) MeSO2Cl, CH2Cl2, RT, 1 h; Et3N, CH2Cl2, RT, 18 h (60%); (d) NH3, MeOH, RT, 2 d (24%); (e) HCl (aq), 110 8C, 2 h (27%).

M. C. Bagley, C. Glover / Tetrahedron 62 (2006) 66–72
69
recorded in the range 4000–600 cmK1 on a Perkin-Elmer
1600 series FTIR spectrometer using KBr disks for solid
samples and thin films between NaCl plates for liquid
samples and are reported in cmK1. Nuclear magnetic
resonance (NMR) spectra were recorded in CDCl3 at
25 8C unless stated otherwise, using either a Bruker DPX
400 or 500 Avance instrument and were reported in ppm; J
values were recorded in Hz and multiplicities were
expressed by the usual conventions (sZsinglet, dZdoublet,
tZtriplet, appZapparent, bZbroad, mZmultiplet). Low-
resolution mass spectra (MS) were determined using a
Fisons VG Platform II Quadrupole instrument using
atmospheric pressure chemical ionization (APcI) unless
stated otherwise. ES refers to electrospray ionization, CI
refers to chemical ionization (ammonia) and EI refers to
electron ionization. High-resolution mass spectra denote the
mass of the ion (mass of electron is 0.00055 Da) unless
stated otherwise. Specific rotations were measured at the
indicated temperature using an AA-1000 (Optical Activity
Ltd) polarimeter at the sodium D line and are given in deg
170.2 (C), 161.4 (C), 147.1 (C), 128.5 (CH), 98.7 (CH), 62.8
(CH2), 61.5 (CH2), 15.1 (Me), 14.4 (Me); m/z (APcI) 260
(MHC, 37%).
3.1.3. Ethyl 2-(dimethoxymethyl)thiazole-4-carboxylate
(14). p-TsOH monohydrate (30 mg, 20 mol%) was added to
a stirred solution of ethyl 2-(diethoxymethyl)thiazole-4-
carboxylate (13) (200 mg, 0.77 mmol) in dry MeOH (5 ml)
and the mixture heated at reflux for 6 h. After evaporating in
vacuo, the mixture was partition between saturated aqueous
NaHCO3 solution (15 ml) and CH2Cl2 (30 ml). The aqueous
layer was further extracted with CH2Cl2 (2!30 ml) and the
organic extracts were combined, dried (Na2SO4) and
evaporated in vacuo. Purification by column chromato-
graphy on SiO2, eluting with EtOAc–light petroleum (1:1)
(Rf 0.41), gave the title compound as a brown oil (118 mg,
66%) (Found: MHC, 232.0638. C9H13NO4S requires MHC,
232.0637); IR (film)/cmK1 nmax 3439, 3106, 2981, 1730,
1454, 1369, 1332, 1248, 1216, 1095, 1021, 950.1, 860, 766;
1H NMR (400 MHz; CDCl3) d 8.14 (1H, s, 5-H), 5.52 (1H,
s, CH), 4.35 (2H, q, JZ7.1 Hz, CH2), 3.39 (6H, s, MeO),
1.34 (3H, t, JZ7.1 Hz, Me); 13C NMR (100 MHz; CDCl3) d
168.9 (C), 161.4 (C), 147.3 (C), 128.6 (CH), 100.3 (CH),
61.6 (CH2), 54.0 (Me), 14.4 (Me); m/z (APcI) 232 (MHC,
73%).
cm3 gK1 dmK1 with concentration c in 10K2 gcmK3
.
Microanalyses were recorded using a Perkin-Elmer 240C
Elemental Analyzer. In vacuo refers to evaporation at
reduced pressure using a rotary evaporator and diaphragm
pump, followed by the removal of trace volatiles using a
vacuum (oil) pump.
3.1.1. 2,2-Diethoxythioacetamide (12). A mixture of
diethoxyacetonitrile (1.12 ml, 8.06 mmol) and ammonium
sulfide (50 wt% in H2O; 1.5 ml, 11.0 mmol) in MeOH
(100 ml) was stirred overnight. The mixture was evaporated
in vacuo to give the title compound as a pale yellow solid
(1.5 g, 100%), mp 92–93 8C (lit.30 mp 81–82 8C) (Found:
MHC, 164.0743. C6H13NO2S requires MHC, 164.0740)
(Found: C, 44.1; H, 8.0; N, 8.4; S, 19.5. Calcd for
C6H13NO2S: C, 44.2; H, 8.0; N, 8.6; S, 19.6%); IR (KBr)/
cmK1 nmax 3371, 3256, 2971, 2916, 1604, 1424, 1368, 1246,
1121, 1057, 960, 918, 824, 724; 1H NMR (400 MHz;
CDCl3) d 7.87 (1H, bs, NH), 7.62 (1H, bs, NH), 5.05 (1H, s,
CH), 3.76 (2H, dq, JZ9.5, 7 Hz, 2OCHH), 3.67 (2H, dq,
JZ9.5, 7 Hz, 2OCHH), 1.18 (6H, t, JZ7 Hz, 2Me); 13C
NMR (125 MHz; CDCl3) d 202.2 (C), 103.0 (CH), 62.9
(CH2), 15.1 (Me); m/z (EI) 163 (MC, 2%), 118 (15), 103
(87).
3.1.4. 2-(Dimethoxymethyl)thiazole-4-carboxylic acid
(15). LiOH monohydrate (108 mg, 2.6 mmol) was added
to a stirred solution of ethyl ester 14 (100 mg, 0.43 mmol) in
MeOH–2O (5:1) (4 ml) and the solution was stirred
overnight. After evaporating in vacuo, the mixture was
partitioned between citric acid (1 M; 8 ml) and CH2Cl2
(35 ml). The aqueous layer was further extracted with
CH2Cl2 (2!20 ml) and the organic extracts were combined,
washed with brine (30 ml), dried (Na2SO4) and evaporated
in vacuo to give the title compound as a brown solid (56 mg,
64%), mp 112–113 8C (EtOAc) (Found: MHC204.0325.
C7H9NO4S requires MHC204.0325); IR (KBr)/cmK1 nmax
3391, 2885, 2698, 2586, 2511, 1726, 1503, 1484, 1459,
1399, 1320, 1205, 1092, 1062, 984, 953, 905, 872, 820, 770,
732, 670; 1H NMR (400 MHz; CDCl3) d 9.40 (1H, bs, OH),
8.25 (1H, s, 5-H), 5.52 (1H, s, CH), 3.36 (6H, s, Me); 13C
NMR (100 MHz; CDCl3) d 168.5 (C), 161.3 (C), 147.4 (C),
129.1 (CH), 100.2 (CH), 53.1 (Me); m/z (APcI) 204 (MHC,
100%).
3.1.2. Ethyl 2-(diethoxymethyl)thiazole-4-carboxylate
(13). Ethyl bromopyruvate (1.71 ml, 13.6 mmol) was
added to a stirred solution of 2,2-diethoxythioacetamide
˚
3.1.5. 2-(Dimethoxymethyl)thiazole-4-carboxylic acid
(15) from 13. p-TsOH monohydrate (300 mg, 156 mmol)
was added to a stirred solution of ethyl 2-(diethoxy-
methyl)thiazole-4-carboxylate (13) (2 g, 7.7 mmol) in
MeOH (60 ml) and the mixture heated at reflux for 6.5 h.
After cooling to room temperature, LiOH monohydrate
(1.9 g, 46 mmol) and water (12 ml) were added and the
solution was stirred for 48 h at room temperature. After
evaporating in vacuo, the mixture was partitioned between
citric acid (1 M; 40 ml) and CH2Cl2 (80 ml). The aqueous
layer was further extracted with CH2Cl2 (2!60 ml) and the
organic extracts were combined, dried (Na2SO4) and
evaporated in vacuo to give the title compound as an off-
white solid (0.85 g, 54%), mp 115–116 8C, with identical
spectroscopic properties.
(12) (1.22 g, 7.47 mmol) in EtOH (16 ml) over 4 A
molecular sieves (14 g) and the mixture was heated at
reflux for 1 h. The solution was allowed to cool, filtered
through Celitew and evaporated in vacuo. Purification twice
by column chromatography on SiO2, eluting with Et2O–
light petroleum (4:1) and Et2O–light petroleum (1:1) (Rf
0.28), gave the title compound as a pale yellow oil (1.94 g,
100%) (Found: MHC, 260.0956. C11H17NO4S requires
MHC, 260.0951); IR (film)/cmK1 nmax 3441, 3113, 2983,
2359, 1694, 1556, 1454, 1391, 1368, 1332, 1216, 1101,
1020, 953, 882, 860, 767, 704; 1H NMR (400 MHz; CDCl3)
8.10 (1H, s, 5-H), 5.63 (1H, s, CH), 4.32 (2H, q, JZ7.1 Hz,
CH2), 3.69 (2H, dq, JZ9.5, 7 Hz, 2OCHH), 3.60 (2H, dq,
JZ9.5, 7 Hz, 2OCHH), 1.35 (3H, t, JZ7.1 Hz, Me), 1.18
(6H, app t, JZ7.1 Hz, Me); 13C NMR (100 MHz; CDCl3) d

70
M. C. Bagley, C. Glover / Tetrahedron 62 (2006) 66–72
3.1.6. Z-L-Thr(TBS)-OMe. Imidazole (1.5 g, 22 mmol),
DMAP (0.92 g, 7.5 mmol) and TBDMSCl (2.3 g, 15 mmol)
were added successively to a solution of Z-L-Thr-OMe
(3.0 g, 11 mmol) in DMF (11 ml). The mixture was stirred
at room temperature for 36 h, acidified with hydrochloric
acid (1 M; 15 ml) and extracted with ether (3!40 ml). The
combined organic extracts were washed with H2O (3!
60 ml), dried (Na2SO4) and evaporated in vacuo to give the
title compound as a pale yellow oil (4.3 g, 100%) (Found:
MHC, 382.2048. C19H31NO5Si requires MHC, 382.2044);
[a]3D0 K6.6 (c2.05, CHCl3) {lit.31 [a]2D4 K7.31 (c3.55,
CHCl3)}; IR (film)/cmK1 nmax 3449, 2954, 2856, 1730,
1507, 1472, 1436, 1378, 1344, 1315, 1255, 1209, 1174,
1129, 1101, 1071, 1030, 1004, 963, 838, 810, 777; 1H NMR
(400 MHz; CDCl3) d 7.35 (5H, PhH), 5.42 (1H, bd, JZ
9.8 Hz, NH), 5.13 (2H, s, CH2O), 4.42 (1H, dq, JZ6.3,
1.7 Hz, b-CH), 4.25 (1H, dd, JZ9.8, 1.7 Hz, a-CH), 3.67
(3H, s, MeO), 1.17 (3H, d, JZ6.3 Hz, Me) 0.8 (9H, s,
CMe3), K0.01 (3H, s, MeSiMe), K0.05 (3H, s, MeSiMe);
13C NMR (100 MHz; CDCl3) d 171.4 (C), 156.8 (C), 136.3
(C), 128.6 (CH), 128.5 (CH), 122.3 (CH), 69.8 (CH), 67.2
(CH2), 59.9 (CH), 52.3 (Me), 25.6 (Me), 20.8 (Me), 17.8
(C), K4.39 (Me), K5.34 (Me); m/z (APcI) 382 (MHC,
100%).
nmax 3446, 3357, 2955, 1752, 1723, 1670, 1507, 1253, 1207,
1132, 1102, 1078, 967, 839, 780; 1H NMR (400 MHz;
CDCl3) d 7.43 (1H, bd, JZ8.8 Hz, NH), 7.20 (5H, PhH),
5.74 (1H, bd, JZ5.7 Hz, NH), 5.01 (1H, d, JZ12 Hz,
CHH), 4.92 (1H, d, JZ12 Hz, CHH), 4.42 (1H, dd, JZ8.8,
1.7 Hz, CHCO2Me), 4.21 (2H, 2b-H), 4.14 (1H, m, a-H),
3.60 (3H, s, Me), 2.05 (1H, bs, OH), 1.05 (3H, d, JZ6.4 Hz,
Me), 1.01 (3H, d, JZ6.2 Hz, Me), 0.78 (9H, s, CMe3), 0.04
(3H, s, MeSiMe), 0.00 (3H, s, MeSiMe); 13C NMR
(100 MHz; CDCl3) d 171.1 (C), 170.1 (C), 156.2 (C),
136.1 (C), 128.6 (CH), 128.2 (CH), 128.1 (CH), 68.4 (CH),
67.6 (CH), 67.0 (CH2), 59.1 (CH), 57.3 (CH), 52.5 (Me),
25.7 (C), 19.9 (Me), 17.9 (Me), 17.4 (Me), K4.8 (Me),
K5.0 (Me); m/z (APcI) 483 (MHC, 100%).
3.1.9. (4S, 5S, 10S, 20R)-Methyl N-(benzyloxy)carbonyl-2-
[1-amino-2-(tert-butyldimethylsilyloxy)prop-1-yl]-5-
methyloxazoline-4-carboxylate (18). [Bis(2-methoxy-
ethyl)amino]sulfur trifluoride (Deoxo-Fluor) (0.37 ml,
2.0 mmol) was added dropwise to a stirred solution of
Z-L-Thr(TBS)-L-Thr-OMe 17 (0.95 g, 1.97 mmol) in dry
CH2Cl2 (30 ml) at K20 8C. The solution was stirred for 18 h
and then quenched by the addition of saturated aqueous
NaHCO3 solution (30 ml). After warming to room
temperature, the mixture was extracted with CH2Cl2 (3!
40 ml). The organic extracts were combined, dried
(Na2SO4) and evaporated in vacuo. Purification by column
chromatography on SiO2, eluting with light petroleum–
EtOAc (Rf 0.39), gave the title compound as a colourless oil
(595 mg, 65%); [a]D32 C7.4 (c1.05, CHCl3); IR (film)/cmK1
nmax 3330, 3034, 2954, 2856, 2358, 1731, 1674, 1504, 1383,
1258, 1212, 1101, 836, 778, 698; 1H NMR (400 MHz;
CDCl3) d 7.33 (5H, PhH), 5.45 (1H, bd, JZ9.5 Hz, NH),
5.11 (1H, d, JZ13.7 Hz, CHH), 5.08 (1H, d, JZ13.7 Hz,
CHH), 4.90 (1H, dq, JZ10.4, 6.3 Hz, 5-H), 4.78 (1H, d, JZ
10.4 Hz, 4-H), 4.42 (1H, d, JZ9.5 Hz, NHCH), 4.35 (1H, q,
JZ6.3 Hz, CH), 3.75 (3H, s, OMe), 1.25 (3H, d, JZ6.3 Hz,
5-Me), 1.17 (3H, d, JZ6.3 Hz, Me), 0.80 (9H, s, CMe3),
0.00 (3H, s, MeSiMe), K0.06 (3H, s, MeSiMe); 13C NMR
(100 MHz; CDCl3) d 170.0 (C), 168.8 (C), 156.4 (C), 136.4
(C), 128.6 (CH), 128.5 (CH), 128.1 (CH), 78.1 (CH), 71.3
(CH), 69.3 (CH), 67.0 (CH2), 55.5 (CH), 52.1 (Me), 25.7
(Me), 20.6 (Me), 17.9 (C), 16.3 (Me), K4.4 (Me), K5.0
(Me); m/z (APcI) 483 (100%), 465 (MHC, 50).
3.1.7. Z-L-Thr(TBS)-OH 16. LiOH monohydrate (1.05 g,
25.0 mmol) was added to a stirred solution of Z-L-
Thr(TBS)-OMe (1.5 g, 3.93 mmol) in MeOH–H2O (5:1)
(40 ml). After stirring for 18 h, the mixture was partitioned
between hydrochloric acid (1 M; 40 ml) and CH2Cl2
(60 ml). The aqueous layer was further extracted with
CH2Cl2 (2!60 ml) and the organic extracts were combined,
dried (Na2SO4) and evaporated in vacuo to give the title
compound as a colourless solid (1.38 g, 96%), mp 149–
150 8C (triturated with light petroleum–EtOAc) (lit.27 mp
154–157 8C) (Found: MHC, 368.1883. C18H29NO5Si
requires MHC, 368.1888); [a]D31 C10.3 (c2.82, CHCl3)
{lit.27 [a]D22 C10.5 (c1.69, CHCl3)}; IR (KBr)/cmK1 nmax
3440, 3035, 2956, 2856, 1702, 1600, 1514, 1455, 1413,
1344, 1308, 1257, 1102, 1042, 1005, 975, 836, 813, 778,
733, 696; 1H NMR (500 MHz; CDCl3) d 9.6 (1H, bs,
CO2H), 7.3 (5H, PhH), 5.43 (1H, bd, JZ8.6 Hz, NH), 5.04
(2H, s, CH2), 4.40 (1H, qd, JZ6.3, 2.4 Hz, b-H), 4.24 (1H,
dd, JZ8.6, 2.4 Hz, a-H), 1.11 (3H, d, JZ6.3 Hz, Me), 0.75
(9H, s, CMe3), K0.02 (3H, s, MeSiMe), K0.03 (3H, s,
MeSiMe); 13C NMR (125 MHz; CDCl3) d 175.7 (C), 156.7
(C), 136.1 (C), 128.6 (CH), 128.3 (CH), 128.2 (CH), 68.5
(CH), 67.3 (CH2), 59.4 (CH), 25.7 (Me), 20.3 (Me), 17.9
(C), K4.6 (Me) and K5.1 (Me); m/z (CI) 368 (MHC, 28%),
277 (100).
3.1.10. (10S, 20R)-Methyl N-(benzyloxy)carbonyl-2-[1-
amino-2-(tert-butyldimethylsilyloxy)prop-1-yl]-5-methyl-
oxazole-4-carboxylate (19). BrCCl3 (0.88 ml, 8.9 mmol) and
DBU (0.88 ml, 5.9 mmol) were added successively to a stirred
solution of the oxazoline 18 (0.60 g, 1.28 mmol) in dry
CH2Cl2 (24 ml) at K20 8C. After stirring for 18 h, the mixture
was poured into saturated aqueous NaHCO3 solution (40 ml)
and extracted with ethyl acetate (3!60 ml). The organic
extracts were combined, dried (Na2SO4) and evaporated in
vacuo. Purification by column chromatography on SiO2,
eluting with light petroleum–EtOAc (Rf 0.63), gave the title
compound as a colourless oil (0.31 g, 52%) (Found:
MHC463.2258. C23H34N2O6Si requires MHC, 463.2259);
[a]3D3 K5.7 (c2.75, CHCl3); IR (film)/cmK1 nmax 3436, 3352,
2954, 2925, 2857, 2361, 1732, 1622, 1587, 1504, 1442, 1352,
1253, 1211, 1100, 965, 915, 838, 810, 778, 739, 698;1H NMR
(400 MHz;CDCl3)d 7.35(5H, PhH), 5.72(1H,bd, JZ9.4 Hz,
NH), 5.15 (2H, s, CH2), 4.93 (1H, dd, JZ9.4, 2.1 Hz, 10-H),
3.1.8. Z-L-Thr(TBS)-L-Thr-OMe 17. Et3N (0.95 ml,
6.8 mmol) was added dropwise over 30 min to a stirred
solution of acid 16 (1.0 g, 2.7 mmol), HCl.H-L-Thr-OMe
(0.509 g, 3.0 mmol) and pyBOP (1.56 g, 3.0 mmol) in dry
CH2Cl2 (13 ml) at 0 8C. The solution was allowed to warm
to room temperature and stirred for a further 18 h. After
concentrating in vacuo, purification by column chromato-
graphy on silica, eluting with light petroleum–EtOAc (1:1)
(Rf 0.49), gave the title compound as a colourless solid
(1.1 g, 83%), mp 133–134 8C (light petroleum–EtOAc)
(Found: MHC, 483.2521. C23H38N2O7Si requires MHC,
483.2521); [a]3D2 C13.1 (c1.05, CHCl3); IR (KBr)/cmK1

M. C. Bagley, C. Glover / Tetrahedron 62 (2006) 66–72
71
4.42 (1H, qd, JZ6.2, 2.1 Hz, 20-H), 3.90 (3H, s, OMe), 2.60
(3H, s, 5-Me), 1.26 (3H, d, JZ6.2 Hz, 20-Me) 0.78 (9H, s,
NH) 5.72 (1H, s, CH), 5.41 (1H, dd, JZ8.9, 2.8 Hz, CH),
4.65 (1H, qd, JZ6.1, 2.8 Hz, CHMe), 4.07 (3H, s, OMe),
3.68 (3H, s, OMe) 3.4 (3H, s, OMe), 2.75 (3H, s, Me), 1.41
(3H, d, JZ6.1 Hz, CHMe), 1.05 (9H, s, CMe3), 0.22 (3H, s,
MeSiMe), 0.03 (3H, s, MeSiMe); 13C NMR (100 MHz;
CDCl3) d 167.9 (C), 162.7 (C), 161.1 (C), 160.7 (C), 156.4
(C), 149.5 (C), 127.5 (C), 125.0 (CH), 100.3 (CH), 70.0
(CH), 54.1 (Me), 53.8 (Me), 53.4 (CH), 52.0 (Me), 25.5
(Me), 20.7 (Me), 17.8 (C), 12.0 (Me), K4.6 (Me), K5.4
(Me); m/z (CIC) 514 (MHC, 95%), 159 (100).
CMe3), 0.03 (3H, s, MeSiMe), K0.17 (3H, s, MeSiMe); 13
C
NMR (100 MHz; CDCl3) d 162.6 (C), 160.9 (C), 156.4 (C),
156.4 (C), 136.2 (C), 128.6 (CH), 128.2, (CH), 127.8 (CH),
127.5 (C), 70.0 (CH), 67.3 (CH2), 55.5 (CH), 52.0 (Me), 25.5
(C), 20.4 (Me), 17.8 (C), 11.9 (Me), K4.7 (Me), K5.5 (Me);
m/z (APcI) 463 (MHC, 100%).
3.1.11. Oxazole 19 from Z-L-Thr(TBS)-L-Thr-OMe 17.
Deoxo-Fluor (0.72 ml, 3.9 mmol) was added dropwise to a
stirred solution of Z-L-Thr(TBS)-L-Thr-OMe 17 (1.87 g,
3.87 mmol) in dry CH2Cl2 (60 ml) at K20 8C. The solution
was stirred for 18 h and then quenched by the addition of
saturated aqueous NaHCO3 solution (30 ml). After warming
to room temperature, the mixture was extracted with
CH2Cl2 (3!100 ml). The organic extracts were combined,
dried (Na2SO4) and evaporated in vacuo to give the crude
oxazoline 18 as a brown oil (2.1 g). The residue was
dissolved in dry CH2Cl2 (70 ml) and cooled to K20 8C.
BrCCl3 (1.7 ml, 17.4 mmol) and DBU (2.6 ml, 17.4 mmol)
were added and the solution was stirred at K20 8C for 18 h.
The mixture was poured into saturated aqueous NaHCO3
solution (70 ml) and extracted with ethyl acetate (3!
60 ml). The organic extracts were combined, dried
(Na2SO4) and evaporated in vacuo. Purification by column
chromatography on SiO2, eluting with light petroleum–Et2O
(Rf 0.15), gave the title compound as a colourless oil (0.94 g,
52%) with identical physical and spectroscopic properties.
3.1.14. Alcohol 22. A solution of TBAF (1.0 M; 1.8 mmol)
in THF (1.8 ml) was added to a stirred solution of silyl ether
21 (580 mg, 1.1 mmol) in dry THF (21 ml) at 0 8C. After
warming to room temperature, the mixture was stirred for
4.5 h and then partitioned between H2O and EtOAc. The
aqueous layer was further extracted with EtOAc (twice) and
the combined organic extracts were dried (Na2SO4) and
evaporated in vacuo. Purification by column chromato-
graphy on SiO2, eluting with EtOAc (Rf 0.31), gave the title
compound as a colourless solid (344 mg, 77%), mp 159–
160 8C (25% EtOAc–light petroleum) (Found:
MHC400.1171. C16H21N3O7S requires MHC, 400.1173);
[a]2D7 K14.7 (c2.3, CHCl3); IR (KBr)/cmK1 nmax 3458,
3277, 3123, 2956, 2825, 2362, 1715, 1668, 1540, 1497,
1453, 1391, 1376, 1334, 1247, 1217, 1192, 1148, 1098,
1
1063, 982, 828, 797; H NMR (400 MHz; CDCl3) d 8.11
(1H, s, CH), 8.03 (1H, d, JZ9.3 Hz, NH) 5.45 (1H, s, CH),
5.24 (1H, dd, JZ9.3, 2.9 Hz, CH), 4.51 (1H, qd, JZ6.3,
2.9 Hz, CHMe), 3.82 (3H, s, OMe), 3.61 (1H, s, OH), 3.37
(6H, s, OMe), 2.53 (3H, s, Me), 1.22 (3H, d, JZ6.3 Hz,
CHMe); 13C NMR (100 MHz; CDCl3) d 168.2 (C), 162.4
(C), 161.3 (C), 160.6 (C), 156.9 (C), 149.3 (C), 127.3 (C),
125.5 (CH), 99.9 (CH), 67.7 (CH), 53.7 (Me), 52.0 (Me),
51.9 (CH), 19.2 (Me), 12.1 (Me); m/z (CIC) 400 (MHC,
100%).
3.1.12. (10S, 20R)-Methyl 2-[1-amino-2-(tert-butyl-
dimethylsilyloxy)prop-1-yl]-5-methyloxazole-4-car-
boxylate (20). A solution of oxazole 19 (0.94 g, 2.0 mmol)
in MeOH (34 ml) was stirred over Pd–C (10 wt%; 817 mg)
under an atmosphere of H2 for 3 h. The mixture was filtered
through Celitew and evaporated in vacuo to give the title
compound as a colourless solid, mp 75–76 8C (623 mg,
93%) (Found: MHC329.1890, C15H28N2O4Si requires
MHC329.1891); [a]D31 K29.3 (c2.78, CHCl3); IR (film)/
cmK1 nmax 3387, 2955, 2857, 1721, 1621, 1441, 1351, 1256,
3.1.15. Methyl sulfomycinate (10). A solution of alcohol
22 (344 mg, 0.86 mmol), Et3N (1.2 ml, 8.6 mmol) and MsCl
(0.53 ml, 6.9 mmol) in dry CH2Cl2 (20 ml) was stirred for
1 h at room temperature. The solution was partitioned
between H2O (45 ml) and CH2Cl2 (30 ml) and the aqueous
layer was further extracted with CHCl3 (2!40 ml). The
combined organic extracts were dried (Na2SO4) and
evaporated in vacuo. The residue was dissolved in dry
CH2Cl2 (20 ml), Et3N (2.0 ml, 14.4 mmol) was added and
the mixture was stirred for 18 h. After evaporating in vacuo,
purification by column chromatography on SiO2, eluting
with EtOAc (Rf 0.44), gave the title compound as a
colourless solid (198 mg, 60%), mp 122–123 8C (EtOAc)
(lit.11 mp 124–124.5 8C) (Found: MHC382.1066.
C16H19N3O6S requires MHC, 382.1067); IR (KBr)/cmK1
nmax 3372, 3116, 2924, 2845, 2363, 2344, 1719, 1684, 1618,
1527, 1469, 1439, 1351, 1233, 1189, 1101, 1062; UV
(MeOH)/nm lmax 246 (log 3 4.40) [lit.11 247 (log 3 4.38)];
1H NMR (400 MHz; CDCl3) d 8.65 (1H, bs, NH), 8.14 (1H,
s, CH) 6.68 (1H, q, JZ7.2 Hz, CH), 5.55 (1H, s, CH), 3.82
(3H, s, OMe), 3.41 (6H, s, OMe), 2.57 (3H, s, Me), 1.84 (3H,
d, JZ7.2 Hz, CHMe); 13C NMR (100 MHz; CDCl3) d 168.1
(C), 162.7 (C), 159.0 (C), 157.5 (C), 156.5 (C), 149.7 (C),
128.9 (CH), 128.1 (C), 125.7 (CH), 122.1 (C), 99.9 (CH),
53.6 (Me), 52.0 (Me), 14.5 (Me), 12.2 (Me); m/z (CIC) 382
(MHC, 100%).
1
1205, 1098, 970, 837.0, 776, 666; H NMR (500 MHz;
CDCl3) d 9–6 (2H, bs, NH), 4.45 (2H, 10,20-H), 3.85 (3H, s,
OMe), 2.53 (3H, s, 5-Me) 1.35 (3H, bs, Me) 0.75 (9H, s,
CMe3), 0.05 (3H, s, MeSiMe), K0.1 (3H, s, MeSiMe); 13
C
(100 MHz; CDCl3) d 164.0 (C), 162.8 (C), 156.3 (C), 127.2
(C), 70.7 (CH), 56.5 (CH), 52.0 Me), 25.7 (Me), 20.5 (Me),
17.8 (C), 11.9 (Me), K4.5 (Me), K5.3 (Me); m/z (APcI)
329 (MHC, 100%).
3.1.13. Amide 21. Et3N (0.50 ml, 3.6 mmol) was added
dropwise over 30 min to a stirred solution of acid 15
(325 mg, 1.6 mmol), amine 20 (420 mg, 1.3 mmol) and
pyBOP (830 mg, 1.6 mmol) in dry CH2Cl2 (13 ml) at 0 8C.
The solution was allowed to warm to room temperature and
stirred for a further 18 h. After concentrating in vacuo,
purification by column chromatography on silica, eluting
with light petroleum–EtOAc (1:1) (Rf 0.31), gave the title
compound as a colourless oil (580 mg, 88%) (Found:
MHC514.2044, C22H35N3O7SSi requires MHC, 514.2038);
[a]2D5 C16 (c2.3, CHCl3); IR (film)/cmK1 nmax 3409, 3116,
2956, 2857, 2400, 1731, 1682, 1621, 1538, 1499, 1471,
1352, 1258, 1186, 1098, 973, 910, 838, 756, 666; 1H NMR
(400 MHz; CDCl3) d 8.3 (1H, s, CH), 8.2 (1H, d, JZ8.9 Hz,

72
M. C. Bagley, C. Glover / Tetrahedron 62 (2006) 66–72
4. Anderson, B.; Hodgkin, D. C.; Viswamitra, M. A. Nature
1970, 225, 233–235.
3.1.16. Sulfomycinic amide (9). A saturated solution of
methanolic NH3 (20 ml) was added to methyl sulfomycinate
(10) (70 mg, 0.18 mmol) at room temperature. The mixture
was stirred at this temperature for 2 days and then
evaporated in vacuo. Purification by column chromato-
graphy on SiO2, eluting with EtOAc, gave the title
compound as a colourless solid (16 mg, 24%), mp 188–
189 8C (EtOAc) (lit.11 mp 194.5–195 8C); (Found:
MHC367.1070. C15H18N4O5S requires MHC, 367.1071);
IR (KBr)/cmK1 nmax 3474, 3360, 3284, 3153, 3090, 2940,
2842, 1687, 1636, 1604, 1555, 1531, 1497, 1482, 1449,
1419, 1369, 1333, 1305, 1229, 1211, 1195, 1168, 1104,
1082, 1042, 1016, 990, 968, 956, 836, 789, 762, 721, 707,
684; 1H NMR (400 MHz; CDCl3) d 8.71 (1H, bs, NH), 8.13
(1H, s, CH) 6.84 (1H, bs, NHH), 6.61 (1H, q, JZ7.2 Hz,
CH), 5.58 (1H, bs, NHH), 5.53 (1H, s, CH), 3.37 (6H, s,
OMe), 2.55 (3H, s, Me), 1.84 (3H, d, JZ7.2 Hz, CHMe);
13C NMR (100 MHz; CDCl3) d 168.2 (C), 164.0 (C), 159.0
(C), 156.7 (C), 153.9 (C), 149.7 (C), 129.4 (C), 128.7 (CH),
125.7 (CH), 122.2 (C), 99.8 (CH), 53.6 (Me), 14.5 (Me),
11.9 (Me); m/z (APcI) 367 (MHC, 18%).
5. Moody, C. J.; Bagley, M. C. Chem. Commun. 1998,
2049–2050.
6. Bagley, M. C.; Bashford, K. E.; Hesketh, C. L.; Moody, C. J.
J. Am. Chem. Soc. 2000, 122, 3301–3313.
7. Hughes, R. A.; Thompson, S. P.; Alcaraz, L.; Moody, C. J.
Chem. Commun. 2004, 946–948.
8. (a) Nicolaou, K. C.; Safina, B. S.; Zak, M.; Estrada, A. A.; Lee,
S. H. Angew. Chem., Int. Ed. 2004, 43, 5087–5092. (b)
Nicolaou, K. C.; Zak, M.; Safina, B. S.; Lee, S. H.; Estrada,
A. A. Angew. Chem., Int. Ed. 2004, 43, 5092–5097.
9. (a) Nicolaou, K. C.; Safina, B. S.; Zak, M.; Lee, S. H.;
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Nevalainen, M.; Bella, M.; Estrada, A. A.; Funke, C.; Zecri,
F. J.; Bulat, S. J. Am. Chem. Soc. 2005, 127, 11159–11175. (b)
Nicolaou, K. C.; Zak, M.; Safina, B. S.; Estrada, A. A.; Lee,
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11176–11183.
10. Egawa, Y.; Umino, K.; Tamura, Y.; Shimizu, M.; Kaneko, K.;
Sakurazawa, M.; Awataguchi, S.; Okuda, T. J. Antibiot. 1969,
22, 12–17.
11. Abe, H.; Takaishi, T.; Okuda, T.; Aoe, K.; Date, T.
Tetrahedron Lett. 1978, 2791–2794.
3.1.17. ( )-Sulfomycinine (7)$HCl (6-carboxy-5-methyl-
8-oxo-5,6,7,8-tetrahydrothiazolo[3,4-a]pyrazinium
chloride). Methyl sulfomycinate (10) (67 mg, 0.76 mmol)
was stirred in hydrochloric acid (6 M; 9 ml) in a Carius tube
at 110 8C for 2 h. After cooling, the mixture was evaporated
in vacuo, by forming an azeotrope with MeOH. The residue
was triturated with MeOH to give the title compound as a
colourless solid (12 mg, 27%), mp 203–204 8C (dec.)
(EtOAc) (lit.12 mp 205–207 8C) (Found: [MK
Cl]C213.0325. C8H8N2O3S.HCl requires [MKCl]C,
213.0328); IR (KBr)/cmK1 nmax 3455, 3197, 3096, 3055,
2370, 2288, 1740, 1686, 1575, 1436, 1192, 887, 761; UV
(MeOH)/nm lmax 230 (log 3 3.76) [lit.12 230 (log 3 3.85)];
1H NMR (500 MHz; D2O) d 10.15 (1H, d, JZ2.4 Hz, exch
D2O, 3-H), 8.77 (1H, d, JZ2.4 Hz, 1-H), 5.51 (1H, dq, JZ
1.5, 6.9 Hz, 5-H), 4.46 (1H, d, JZ1.5 Hz, 6-H), 1.61 (3H, d,
JZ6.9 Hz, Me); 13C NMR (125 MHz; D2O) d 172.3 (C),
159.7 (CH), 156.7 (C), 136.1 (C), 131.5 (CH), 59.8 (CH),
57.5 (CH), 19.6 (Me); m/z (ES) 215 ([MKCl]C, 100%).
12. Abe, H.; Ikeda, M.; Takaishi, T.; Ito, Y.; Okuda, T.
Tetrahedron Lett. 1977, 735–736.
13. Abe, H.; Kushida, K.; Shiobara, Y.; Kodama, M. Tetrahedron
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14. Kohno, J.; Kameda, N.; Nishio, M.; Kinumaki, A.;
Komatsubara, S. J. Antibiot. 1996, 49, 1063–1065.
¨
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17. Bagley, M. C.; Chapaneri, K.; Dale, J. W.; Xiong, X.; Bower,
J. J. Org. Chem. 2005, 70, 1389–1399.
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Acknowledgements
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We thank the Royal Society and EPSRC (GR/S 25456/01)
for their generous support, Robert L. Jenkins for technical
assistance and the EPSRC Mass Spectrometry Service,
Swansea UK, for high resolution spectra.
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