ライフサイエンスコーパス: hemiacetal

1 is driven to completion by cyclization to a hemiacetal.

2 on of an intermediate flavin C4a-hydroperoxy hemiacetal.

3 y labile intermediates to racemic versiconal hemiacetal.

4 on of a bicyclic isoxazolidine-derived azido-hemiacetal.

5 stabilized phosphorus ylide bearing an omega-hemiacetal.

6 otolyzed without involvement of a long-lived hemiacetal.

7 em had a carbonyl group in a free form or as hemiacetal.

8 wo aldehyde groups, one of which exists as a hemiacetal.

9 st in equilibrium with stereoisomeric cyclic hemiacetals.

10 The phosphorylated cyclic hemiacetals 1 and 2 were isolated as binary mixtures of

11 zation, rearrangement, and ring expansion of hemiacetal, 15, is proposed.

12 H followed by reduction with thiourea led to hemiacetal 22.

13 Hence, the sodium borohydride reduction of hemiacetals 2a,b can be controlled to give either a bicy

14 The addition of allylindium to hemiacetals 2a,b occurs both regio- and diastereoselecti

15 during the sulfoxide-catalyzed conversion of hemiacetal 3 to glycosyl sulfonate 10.

16 7 was introduced leading to a mixture of the hemiacetals 48 and the corresponding ketone 49.

17 ton of the hydroxyl residue of the substrate hemiacetal 6-OH group.

18 n stimulated with motilin, erythromycin, 6,9-hemiacetal 8,9-anhydro-4''-deoxy-3'-N-desmethyl-3'-N-eth

19 Hemiacetal 9 can be converted to an acetal, reduced to a

20 e conversion of averufin (AVF) to versiconal hemiacetal acetate (VHA), in Aspergillus parasiticus and

21 perturbations, provides strong evidence that hemiacetal activation proceeds through initial nucleophi

22 Mechanistic studies focused on the hemiacetal activation process show that this transformat

23 The X-ray crystal structure of the hemiacetal adduct between Ser 195 of chymotrypsin and N-

24 se Bis-Acetal-Based Substrates (BABS) bear a hemiacetal aglycon leaving group that tethers fluorochro

25 xist as an equilibrating mixture of a cyclic hemiacetal and a ring-opened aldehyde.

26 The protonation states of the hemiacetal and His 57 are explained by the high basicity

27 y 1H NMR indicates that isomerization of the hemiacetal and/or hemiketal is rapid.

28 the glycosylation between 2,6-dideoxy-sugar hemiacetals and glycosyl acceptors in good yield and hig

29 and aldehyde, and they show the formation of hemiacetals and hemiketals on binding small guests with

30 te donors are prepared in situ from glycosyl hemiacetals, and are coupled under mild, operationally s

31 We found that formaldehyde hemiacetals are a considerable fraction of the total for

32 The structures of the bound hemiacetals are determined by 1D and 2D NMR studies.

33 Although the health effects of the hemiacetals are not yet known, they warrant further inve

34 oacetate with a difluorinated aldehyde ethyl hemiacetal as a key step.

35 and reductive ring opening of the resulting hemiacetal as the key steps.

36 nstrates that use of promoters that activate hemiacetals as well-defined intermediates can be used to

37 th chymotrypsin is consistent with a neutral hemiacetal between pH 7 and 13.

38 teraction between the hydroxyl oxygen at the hemiacetal C1 of GAP and the nicotinamide ring.

39 dducts in the R- and S-configurations at the hemiacetal carbons.

40 At pH <7.0, His 57 in the AcLF-CHO-hemiacetal complex of chymotrypsin undergoes protonation

41 The formaldehyde hemiacetals derived from these solvents were reported as

42 These cyclic hemiacetals effectively mask the reactive aldehydes nece

43 The reason for this is that formaldehyde hemiacetals follow other reaction pathways, such as the

44 converting the C-1 anomeric carbon into free hemiacetal followed by intramolecular reductive aminocyc

45 ially available trifluoroacetaldehyde methyl hemiacetal, followed by a classical chemical resolution,

46 conjugate addition, leading to chiral cyclic hemiacetals, followed by a multicomponent reaction with

47 (10%), monohydrated acyclic (5%), and cyclic hemiacetal form (85%) of orthophthalaldehyde (OPA).

48 nfiguration of the C1' hydroxyl group of the hemiacetal form on duplex structure and abasic site repa

49 s in a carbohydrate-like fashion in a cyclic hemiacetal form under aprotic conditions.

50 ther the abasic site is in the alpha or beta hemiacetal form.

51 sing or decreasing the product pH, to induce hemiacetal formation and acetal stabilization or induce

52 significant role in oligomer formation, with hemiacetal formation less important, and aldol condensat

53 ation after changing CysI to serine suggests hemiacetal formation.

54 -hand with a stabilizing O-methylation and a hemiacetal formation.

55 mechanism in which the hydroxyl group of the hemiacetal formed upon addition of methanol to the aldeh

56 the aldehyde, the hydrated aldehyde, and the hemiacetal forms (dominant).

57 trolled dehydrative coupling of various C(1)-hemiacetal glycosyl donors and nucleophilic acceptors pr

58 yclic carbohydrates, with and without a free hemiacetal group, is observed.

59 en established in the context of a versatile hemiacetal hydroxyl activation/substitution reaction for

60 through initial nucleophilic addition of the hemiacetal hydroxyl to the S(IV)-center of putative sulf

61 sual tetrahydrofuran ring with a concomitant hemiacetal in its structure.

62 The presence of these cyclic hemiacetals in duplex DNA is significant as they mask th

63 nesulfonic anhydride activates 2-deoxy-sugar hemiacetals in situ as electrophilic species, which reac

64 abilize the transition state oxyanion of the hemiacetal intermediate in support of the flip-flop mode

65 resolved UV-vis measurements showed that the hemiacetal intermediate is formed by two competing pathw

66 A superposition of NAD(+)-bound and hemiacetal intermediate structures reveals an interactio

67 , consistent with synthesis of a short-lived hemiacetal intermediate that breaks down spontaneously i

68 ciated H-bond, and the crucial ferric peroxo-hemiacetal intermediate that precedes carbon-carbon (C-C

69 ver, proton-assisted homolysis of the peroxo hemiacetal intermediate to produce P450 compound I and t

70 aliphatic alcohols showed that a long-lived hemiacetal intermediate was formed during the reaction.

71 h a dynamic kinetic resolution of the peroxy hemiacetal intermediate.

72 illman reaction involving the formation of a hemiacetal intermediate.

73 matic states, NAD(+)-free, NAD(+)-bound, and hemiacetal intermediate.

74 Hemiacetal intermediates for the rate-limiting proton tr

75 ydrolysis of benzaldehyde dialkyl acetals to hemiacetal intermediates that breakdown rapidly to benza

76 dehydes, and ketones through the collapse of hemiacetal intermediates.

77 es confirm that, under these conditions, the hemiacetal is quantitatively converted into an alpha-gly

78 classic acid-catalyzed hydrolysis, where the hemiacetal is the putative intermediate responsible for

79 BS) in which a racemic substrate, versiconal hemiacetal, is cyclized to an optically active product w

80 We find the hemiacetal leaving group rapidly breaks down, enabling q

81 f CysI by alanine, which cannot form a (thio)hemiacetal, led to even higher activities, pointing to a

82 Surprisingly, the (R) stereochemistry at the hemiacetal linkage is opposite to that expected by compa

83 Hydrolysis of the hemiacetal linkage of some of these modified carbohydrat

84 The hemiacetal linkages to the essential Ser146 are of a sin

85 The bismuth-mediated two-component hemiacetal/oxa-conjugate addition of delta-trialkylsilyl

86 57 are explained by the high basicity of the hemiacetal oxygen (pK(a) > 13.5) relative to that of His

87 oton from solution, it is concluded that the hemiacetal oxygen of the chymotrypsin-AcLF-CHO complex i

88 In the (R)-hemiacetal, oxygen is hydrogen bonded to His 57, not the

89 erating in this multistep domino-aldol-aldol-hemiacetal protocol was used for probing the efficiency

90 The domino-aldol-aldol-hemiacetal-reaction cascade of indium and other group 13

91 oxyl hydroperoxide intermediates followed by hemiacetal ring closure.

92 as determined that these compounds contained hemiacetal ring structures and two double bonds, as woul

93 lesterol by nucleophilic addition, forming a hemiacetal salt.

94 eated with hydrochloric acid to liberate the hemiacetal shown.

95 site hole and assists in the opening of the hemiacetal, shows conformational exchange.

96 eavage of the glycosidic bond, the liberated hemiacetal spontaneously breaks down, leading to separat

97 formation of acetal to aldehyde occurs via a hemiacetal TFA ester intermediate, which differentiates

98 chlorophenoxyacetic acid (2,4-D) producing a hemiacetal that spontaneously decomposes to 2,4-dichloro

99 d less nucleophilic than that derived from a hemiacetal, the nondirected reaction is much slower for

100 rom the refined structures of the two cyclic hemiacetals, the conformations of the corresponding dias

101 two equilibrating enantiomers of versiconal hemiacetal to cyclize the appropriate antipode to optica

102 side chain cyclization of racemic versiconal hemiacetal to the bisfuran ring system of(-)-versicolori

103 The azido-hemiacetal was also converted into an aza-C-glycoside im

104 e 5'-direction, while the (6R,8S,11R) cyclic hemiacetal was oriented in the 3'-direction.

105 The (6S,8R,11S) cyclic hemiacetal was oriented in the 5'-direction, while the (

106 ereomeric (6S,8R,11S) and (6R,8S,11R) cyclic hemiacetals were examined with respect to conformation w

107 the study described herein, the formaldehyde hemiacetals were found at higher levels than those of fr

108 Both the (6S,8R,11S) and (6R,8S,11R) cyclic hemiacetals were located within the minor groove of the

109 oth exist primarily as diastereomeric cyclic hemiacetals when placed into duplex DNA.

110 he abasic site in CD is predominantly a beta hemiacetal, whereas in AD the alpha and beta forms are e

111 hi cross-coupling affording an omega-hydroxy hemiacetal which was macrocyclized via a domino addition

112 hen rapidly adds to the enol ether to form a hemiacetal, which then undergoes elimination to cyclohex

113 ive ("parasitic") intermediate, namely a N,O-hemiacetal with trifluoroacetophenones.

114 he respective orientations of the two cyclic hemiacetals within the minor groove were dependent upon