A 15-step synthesis of (+)-ryanodol

Article abstract of DOI:10.1126/science.aag1028

(+)-Ryanodine and (+)-ryanodol are complex diterpenoids that modulate intracellular calcium-ion release at ryanodine receptors, ion channels critical for skeletal and cardiac muscle excitation-contraction coupling and synaptic transmission. Chemical derivatization of these diterpenoids has demonstrated that certain peripheral structural modifications can alter binding affinity and selectivity among ryanodine receptor isoforms. Here, we report a short chemical synthesis of (+)-ryanodol that proceeds in only 15 steps from the commercially available terpene (S)-pulegone. The efficiency of the synthesis derives from the use of a Pauson-Khand reaction to rapidly build the carbon framework and a SeO2-mediated oxidation to install three oxygen atoms in a single step. This work highlights how strategic C-O bond constructions can streamline the synthesis of polyhydroxylated terpenes by minimizing protecting group and redox adjustments.

Full text of DOI:10.1126/science.aag1028

RESEARCH
◥
sequence (28), providing the target molecule in
41 total steps (37 steps in its longest linear se-
quence). A more recent series of studies from
Inoue and co-workers highlighted the utility of
several radical-based C–O and C–C bond-forming
reactions in a total synthesis that furnishes ( )-2
(29) and ( )-4 (22), each in 35 total steps. These
studies allowed Inoue et al. to correctly reassign
the structure of the natural product isolated from
P. indica (18) as C3-epi-ryanodol (4). Inoue and co-
workers subsequently reported that their synthe-
sis could be rendered enantioselective through a
catalytic asymmetric desymmetrization process
and that an appropriately protected derivative of
(+)-2 could be elaborated to (+)-1 in five synthetic
steps (30, 31). In addition to these total syntheses,
several medicinal chemistry studies have focused
on the derivatization of ryanodine and ryanodol
(32–34). Here, we disclose a direct and concise
strategy to access the central ryanoid ring system,
which has enabled the chemical synthesis of
(+)-ryanodol (2) in only 15 steps from commercially
available starting materials. These studies pro-
vide a synthetic platform from which it will be
possible to prepare previously inaccessible ryanoid
derivatives.
Perhaps the most substantial synthetic chal-
lenge embedded within the structure of 2 is the
highly oxidized five-membered A-ring, which bears
an all-carbon quaternary center and four ad-
ditional stereogenic carbons bonded to oxygen
(Fig. 1A). A concise synthesis of 2 requires a care-
fully choreographed introduction of these moieties
to minimize redox, protecting group, and func-
tional group transformations. Guided by the land-
mark studies of Deslongchamps and co-workers
(28), we identified the C1–C15 bond of ryanodol (2)
as the most simplifying and strategic initial retro-
synthetic disconnection (Fig. 1B). This analysis
revealed the tetracyclic lactone anhydroryanodol
(3) as our initial synthetic target (Fig. 1C), with the
isopropyl group introduced at a late stage through
a transition metal–catalyzed cross-coupling re-
action of enol triflate 6; this approach would
also allow for versatile incorporation of alterna-
tive carbon-based fragments to facilitate long-
term goals of preparing ryanoid derivatives. We
anticipated that the requisite A-ring oxidation
pattern could be accessed via chemo- and stereo-
selective functionalization of cyclopentenone 7,
whereby the enone would provide a functional
group handle to install the critical C3, C4, and
C12 alcohols of 2. We envisioned preparing cyclo-
pentenone 7 by an intramolecular Pauson-Khand
reaction (35), a transformation that would be facili-
tated by the conformational rigidity of bicyclic
lactone 8. Lactone 8 could arise through a series
of transformations from (S)-pulegone, a com-
mercially available terpene. By this analysis, the
oxygen atoms at C6, C10, and C11 would be in-
corporated early in the synthesis, whereas the
oxygen atoms at C3, C4, and C12 would be in-
troduced at a late stage. With the implementation
of appropriate protecting groups, we anticipated
that this strategy would minimize synthetic manip-
ulations ancillary to the direct construction of
the natural product.
REPORTS
ORGANIC SYNTHESIS
A 15-step synthesis of (+)-ryanodol
Kangway V. Chuang,* Chen Xu,* Sarah E. Reisman†
(+)-Ryanodine and (+)-ryanodol are complex diterpenoids that modulate intracellular calcium-ion
release at ryanodine receptors, ion channels critical for skeletal and cardiac muscle
excitation-contraction coupling and synaptic transmission. Chemical derivatization of these
diterpenoids has demonstrated that certain peripheral structural modifications can alter
binding affinity and selectivity among ryanodine receptor isoforms. Here, we report a short
chemical synthesis of (+)-ryanodol that proceeds in only 15 steps from the commercially
available terpene (S)-pulegone. The efficiency of the synthesis derives from the use of a
Pauson-Khand reaction to rapidly build the carbon framework and a SeO2-mediated
oxidation to install three oxygen atoms in a single step. This work highlights how strategic C–O
bond constructions can streamline the synthesis of polyhydroxylated terpenes by minimizing
protecting group and redox adjustments.
erpenes are a large and structurally diverse
family of natural products that range from
simple hydrocarbons associated with flavors
and fragrances, to complex, highly oxidized
polycyclic molecules such as the antimalarial
pression of RyR2 and RyR3 has been associated
with the pathogenesis of neurodegenerative dis-
orders such as Alzheimer’s disease (13). Ryan-
odine binds with high affinity to the conducting
state of RyRs, exerting concentration-dependent
modulation of Ca2+ release: At nanomolar con-
centrations, ryanodine locks RyRs in an open,
subconductance state, whereas at higher con-
centrations, ryanodine causes closure of the chan-
nels (14). The deacylated compound ryanodol
binds with lower affinity than 1 to mammalian
RyRs; however, it still induces a subconductance
state and has been reported as a reversible probe
of RyR-mediated Ca2+ release in cells (15).
Since the initial reports describing the isolation
of ryanodine from Ryania, a number of con-
geners (known as ryanoids) that vary in oxidation
pattern have been isolated (16–20). Whereas
ryanodol—the compound obtained by hydrolysis
of ryanodine—has not yet been isolated directly
from a natural source, the closely related compound
C3-epi-ryanodol (4) was isolated by Gonzaléz-
Coloma from Persea indica (18). Indeed, owing to
their structural similarities, C3-epi-ryanodol (4)
was initially erroneously reported to be ryanodol
(2); however, the structure of the Coloma-Gonzaléz
isolate (21) was recently reassigned through the
synthetic efforts of Inoue (see below) (22). These
subtle differences in structure exert a pronounced
effect on RyR binding: C3-epi-ryanodine (5),
prepared from 4, binds to RyRs with an affinity
1/100th that of 1 (23).
T
drug artemisinin, and the anticancer compounds
ingenol and taxol (1). Although terpenes are iso-
lated from natural sources, it can be challenging
to translate their biological activity into a prac-
tical application (2). In some cases, the hurdle is
low natural abundance; at other times, it is the
difficulty encountered by chemists seeking to
precisely edit a terpene’s molecular structure to
improve its drug-like properties or interrogate its
role in modulating disease pathways. The devel-
opment of concise chemical syntheses of terpenes
can transform our ability to use these molecules
and their synthetic derivatives as biological probes
or as lead compounds for the development of new
medicines (3–5). Furthermore, these scientific efforts
often innovate chemical reactivity or synthetic
design concepts (6).
The natural product ryanodine (1) (7, 8) and
its hydrolysis product ryanodol (2) (8, 9) are
among the most highly oxidized and synthetically
challenging diterpenoids reported to date (Fig. 1A).
Isolated from the tropical shrub Ryania speciosa
Vahl in connection with its insecticidal properties
(7), ryanodine is the namesake ligand of the ryan-
odine receptors (RyRs) (10), an important family
of ion channels that regulate intracellular Ca2+
release and play a critical role in signal transduc-
tion (11). In mammalian cells, these receptors exist
in multiple isoforms (RyR1, RyR2, and RyR3) that
serve to mediate both movement and cognitive
function. Mutations of RyRs are associated with
genetic diseases such as malignant hyperthermia
and central core disease (12), whereas altered ex-
Given the biological importance of the RyRs,
the ryanoids have been the focus of both total
synthesis and derivatization efforts. In 1979,
Deslongchamps and co-workers disclosed a total
synthesis of (+)-2, which hinged on a key Diels-
Alder cycloaddition and a series of elegantly de-
signed intramolecular aldol reactions to assemble
the tetracyclic ABCD framework (Fig. 1B) (24–28).
In a classic example of relay synthesis, the deg-
radation product (+)-anhydroryanodol (3) was
converted to (+)-ryanodol (2) in a final two-step
Division of Chemistry and Chemical Engineering, California
Institute of Technology, Pasadena, CA 91125, USA.
*These authors contributed equally to this work. †Corresponding
author. Email: reisman@caltech.edu
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RESEARCH
| REPORTS
We first investigated the stereoselective oxida-
tion of (S)-pulegone (10) to install the C6 and C10
alcohols of the C-ring (Fig. 2), envisioning func-
tionalization at both carbons via enolates accessed
by g- or a′-deprotonation of the ketone, respec-
tively. Preliminary experiments confirmed that
the C6-alcohol could be installed with 2.5:1 dia-
stereomeric ratio (dr) through generation of the
thermodynamic dienolate with potassium hexa-
methyldisilazide (KHMDS) followed by quenching
with oxaziridine 11 (36). Noting that KHMDS did
not appear to directly react with oxaziridine 11 at
–78°C, we hypothesized that a one-step protocol
involving excess KHMDS and 11 might simulta-
neously install both alcohols. Indeed, treatment
of 10 with 2.5 equivalents (equiv.) of KHMDS at
–78°C followed by dropwise addition of 2.4 equiv.
of 11 provided a,a′-diol 12, which could be
isolated as a single diastereomer in 42% yield
(120 mmol scale). Although the yield is modest,
this single transformation converts a simple terpene
to a valuable building block with the requisite
ryanodol C-ring oxidation pattern. We improved
the efficiency of this transformation to 50% yield
by modification of the standard procedure on a
smaller scale (10 mmol, see supplementary mate-
rials). However, given the operational simplicity
of the former procedure on larger scales, this pro-
tocol was preferentially employed for increased
material throughput.
Treatment of diol 12 with excess benzyl chloro-
methyl ether effected protection of both alcohols
as benzyloxymethyl ethers to give 13. At this stage,
the D-ring was constructed by an efficient four-step
sequence. First, addition of propynylmagnesium
bromide to 13 at 0°C proceeded in 5:1 dr, providing
the equatorially disposed alkyne in 81% isolated
yield. Ozonolytic cleavage of the 1,1-disubstituted
olefin proceeded in high yield to afford methyl ke-
tone 14. AlthoughaN, N′-dicyclohexylcarbodiimide-
mediated phosphonoacylation and intramolecular
Horner–Wadsworth–Emmons lactone synthesis
had proved moderately effective in model studies
lacking C10 oxidation, the tertiary alkynol of 14
proved resistant to acylation under a number of
conditions. Presumably, the increased steric en-
cumbrance and inductively withdrawing C10-ether
sharply decreases the nucleophilicity of the tertiary
alkynol. Instead, ketone 14 was efficiently con-
verted to a,b-unsaturated lactone 15 via1,2-addition
of ethoxyethynylmagnesium bromide followed
by an Ag-catalyzed cyclization and elimination
cascade (37).
Fig. 1. Ryanodine and selected ryanoids. (A) Chemical structures of (+)-ryanodine (1), (+)-ryanodol
(2), (+)-anhydroryanodol (3), 3-epi-ryanodol (4), and 3-epi-ryanodine (5). (B) Carbon numbering and ring
system letter assignment. (C) Retrosynthetic analysis of anhydroryanodol.
With lactone 15 in hand, 1,4-addition of mag-
nesium divinyl cuprate provided the corresponding
enyne 16 as a single diastereomer in 84% yield,
forging the critical all-carbon quaternary center
at C5 while simultaneously setting the stage
for a key Pauson-Khand cyclization. A number
of Pauson-Khand procedures were screened
for their ability to deliver 17 in both high yield
and diastereoselectivity (Table 1). Although stan-
dard conditions (38, 39) using stoichiometric
amounts of Co2(CO)8 produced the desired pro-
duct, separation of diastereomeric enone 17′
proved challenging and indicated that a more
selective protocol was necessary. Monometallic
Table 1. Evaluation of Pauson-Khand reaction conditions.
.E..n...t..r..y...........................................................................................................................................................................................................
Conditions*
Co2(CO)8 (1.2 equiv.), THF, 12 hours; then DMSO, 65°C
Co2(CO)8 (1.2 equiv.), CH2Cl2, 9 hours; then NMO, 23°C
Mo(CO)6 (1.2 equiv.), DMSO, PhMe, 110°C
dr†
Yield (%)‡
46
1
...................................................................................................................................................................2.....2...:.1..........................................
.2...................................................................................................................................................................4.....5..:.1..........................................
78
3
–
Trace
.....................................................................................................................................................................................................................
4
Mo(CO)3(DMF)3 (1.1 equiv.), CH2Cl2, 23°C
..................................................................................................................................................................>...2...0...:.1.........................................
67
.5..............................[..R...h..C....l.(..C...O...)..2..]..2....(.1....m....o...l..%.....)..,..C...O.....(..1...a...t..m....)..,..m....-..x..y...l.e..n...e...,..1..1..0...°..C.....................>...2...0...:.1.........................................
85
*Reactions conducted on 0.2 mmol scale. THF, tetrahydrofuran; DMSO, dimethylsulfoxide; NMO, N-
methylmorpholine N-oxide; DMF, N,N-dimethylformamide. †Determined by 1H-NMR spectroscopy. ‡Isolated
yield after purification by silica gel chromatography.
SCIENCE sciencemag.org
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RESEARCH
| REPORTS
Fig. 2. Complete synthetic sequence for the chemical synthesis of
(+)-anhydroryanodol and (+)-ryanodol. Reagents and conditions as follows:
1. potassium hexamethyldisilazide (2.5 equiv.),THF –78°C; then 11 (2.4 equiv.), 42
to 50% yield. 2. Benzyl chloromethyl ether (5.0 equiv.), iPr2NEt (8.0 equiv.),
nBu4NI (2.0 equiv.), CH2Cl2, 50°C, 65% yield. 3. Propynylmagnesium bromide,
THF, 0°C, 81% yield, 5:1 dr.4.O3/O2, CH2Cl2/MeOH (4:1), –78°C; then PPh3, 91%
yield. 5. Ethoxyethynylmagnesium bromide (5.0 equiv.),THF, 0°C, 75% yield.
6. AgOTf (2 mol %), PhMe, 0°C, 90% yield. 7. CuI (3.0 equiv.), vinylmagnesium
bromide (6.0 equiv.),THF, –78° to –30°C, 84% yield. 8. [RhCl(CO)2]2 (1 mol %),
CO (1 atm), m-xylene, 110°C, 85% yield. 9. SeO2 (10 equiv.), 4 Å MS,
1,4-dioxane, 110°C. 10. Comins’ reagent, iPr2NEt, CH2Cl2, –78° to 0°C,
28% yield, two steps. 11. PdCl2(PPh3)2, tributyl(prop-1-en-2-yl)stannane,
LiCl, 2-MeTHF, 85°C, 64% yield. 12. LiBH4, THF, –15° to –10°C; then KHF2/
MeOH. 13. H2, Pd(OH)2/C, EtOH, 61% yield, two steps. 14. Trifluoroacetic
anhydride, urea hydrogen peroxide, Na2HPO4, 86% yield. 15. Li0 wire,
NH3/THF, –78°C, 38% yield.
mediators were found to improve the dr, with
Mo(CO)3(DMF)3 (40) providing 17 as a single
diastereomer in 67% yield. Despite the service-
able yield and scalability of this transformation,
we sought a more efficient protocol that could
obviate the need for stoichiometric metals and
their attendant by-products. Treatment of 16
with 1 mol % [RhCl(CO)2]2 (41) under an at-
mosphere of carbon monoxide provided the
desired product in 85% yield, again as a single
diastereomer. This reaction has been conducted
on a multigram scale, providing 5.7 g of enone
17 in a single pass. Single-crystal x-ray diffrac-
tion analysis of 17 confirmed both the absolute
configuration and structural assignment of this
key tetracyclic intermediate.
The successful realization of the Pauson-Khand
cyclization led us to the next phase of our synthetic
studies: chemo- and stereoselective functional-
ization of the A-ring through the introduction of
the C3, C4, and C12-alcohols, as well as the C2-
isopropyl unit. To this end, initial investigations
were aimed at oxidation of the C4 allylic methine
of 17, but efforts in this vein were thwarted by un-
desired reactivity. For example, established methods
for allylic oxidation via reactive radical species
[e.g., Pd(OH)2/C/t-BuOOH (42) or Rh2(cap)4/t-
BuOOH (43)] were unfruitful owing to competi-
fully oxidized diosphenol 18, a compound with
the C4, C12 syn-vicinal diol of 2. This single-step
transformation installs the necessary oxygen
atoms at C3, C4, and C12 while simultaneously
providing a functional group handle for in-
corporation of the C2-isopropyl group.
tive functionalization of the C1–C12 olefin (i.e.,
epoxidation, 1,2-difunctionalization). Although we
considered the possibility of advancing these un-
anticipated products further in the synthesis, it
was unclear how to achieve efficient transposi-
tion to the requisite oxidation pattern.
Because C4-deoxy analog of ryanodine is itself
a natural product, deoxyspiganthine (20), and
could be of interest for future biological studies,
we optimized procedures to prepare both 18
and 21 (Fig. 3). Given concerns that contamina-
tion by 1H–nuclear magnetic resonance (1H-NMR)
silent, red selenium by-products resulted in arti-
ficially inflated isolated yields, our optimization
efforts were guided by 1H-NMR yields determined
by integration versus an added standard. Iso-
lated yields were determined after conversion
to corresponding enol triflates 19 and 22, which
could be obtained as analytically pure com-
pounds. Thus, subjection of tetracycle 17 to
10 equiv. of SeO2 in wet 1,4-dioxane at 110°C
Instead, we turned to C3-functionalization of
17 using SeO2 (44), anticipating that the enone
might be readily oxidized to the corresponding
a-diketone (Fig. 3). We found that treatment of
17 with excess SeO2 in wet 1,4-dioxane at 110°C
not only effected C3-oxidation, but also the for-
mal hydration of the enone, thereby installing
the necessary C12-alcohol and providing dios-
phenol 21. Hypothesizing that rigorous exclusion
of water might promote C4-allylic hydroxyla-
tion before diketone formation, we subjected
enone 17 to SeO2 under anhydrous conditions
in the presence of 4 Å molecular sieves (4 Å MS).
Prolonged heating at 110°C in 1,4-dioxane pro-
vided a distinct product, which had incorporated
an additional oxygen as determined by mass
spectrometry analysis. Rigorous structural as-
signment of this compound revealed it to be the
1
for 1 hour provided 21 in 67 to 69% H-NMR
yield, and the corresponding vinyl triflate 22 in
56% isolated yield over two steps. Alternatively,
treatment of 17 with 10 equiv. of SeO2 in an-
hydrous 1,4-dioxane in the presence of freshly
914 26 AUGUST 2016 • VOL 353 ISSUE 6302
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| REPORTS
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Fig. 3. Selenium dioxide-mediated A-ring oxidation. In the presence of water, SeO2-mediated
oxidation of enone 17 provides 21. In the absence of water, further oxidation occurs to deliver 18.
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activated 4 Å MS at 110°C for 9 hours provided
18 in 33 to 35% 1H-NMR yield, and vinyl triflate
19 in 28% isolated yield over two steps. Despite
the modest yield, this sequence accomplishes the
stereospecific incorporation of three oxygen atoms,
proceeds with an average efficiency of ~70% yield
per transformation, and fares well in comparison
to conceivable multiple step protocols to achieve
the same reactivity. Although the precise mech-
anism of the SeO2-mediated oxidation remains
unclear at this time, investigations are ongoing
and should aid the development of a more
efficient protocol.
The concise synthesis of (+)-ryanodol described
here proceeds in only 15 synthetic steps (0.42%
overall yield) from (S)-pulegone (10), fewer than
half the steps of the previously disclosed syntheses
by Deslongchamps et al. (37 linear steps, 0.23%
yield) and Inoue et al. (35 linear steps, 0.008%
yield). The efficiency of our approach derives
from the development of a direct and scalable
route to key cyclopentenone 17, which can be
prepared on a multigram scale in only eight steps
and rapidly elaborated to (+)-anhydroryanodol.
The strategic use of C–O bond–forming reac-
tions minimizes redox adjustments and the use
of protecting groups. Indeed, the five alcohols
found in (+)-3 are incorporated with just two
transformations: the dihydroxylation of 10 and
the SeO2-mediated oxidation of enone 17. More-
over, all but the C3-alcohol are introduced with
the correct carbon oxidation level. We anticipate
that the brevity of the synthesis will render fea-
sible the design and preparation of ryanoid de-
rivatives for studying RyR function.
In the final stages of the synthesis, advance-
ment of 19 to (+)-anhydroryanodol was achieved
by a three-step sequence. Palladium-catalyzed
cross-coupling between 19 and tributyl(2-propenyl)
stannane installed the final three carbons, de-
livering 20 in 64% yield. LiBH4-mediated 1,2-
reduction stereoselectively furnished the C3
alcohol, which was subjected to H2 and Pd(OH)2/
C to simultaneously reduce the disubstituted
olefin and remove the benzyloxymethyl groups,
providing (+)-3 in 61% yield over two steps.
Using this route, we have prepared >400 mg
of (+)- anhydroryanodol to date. Conversion of
this material to (+)-ryanodol was achieved via a
slight modification of Deslongchamps’s two-step
protocol (28). Treatment of 3 with trifluoroper-
acetic acid, freshly prepared from trifluoroacetic
anhydride and urea hydrogen peroxide (in place
of the originally reported concentrated hydro-
gen peroxide), cleanly afforded epianhydrorya-
nodol epoxide in 86% yield. Subjection of this
material to Li0 in NH3 (distilled from Na0) at
–78°C resulted in reductive cyclization to pro-
duce (+)-2 in 38% yield (lit. 60% yield). In our
hands, the reaction profile was highly dependent
on the purity of the ammonia. Specifically, in-
dependent control reactions conducted with
ammonia condensed directly from the gas cyl-
inder, or using redistilled ammonia with either
added H2O (10 equiv.), or exogenous Fe-salts
(45), revealed that these parameters all substan-
tially affect the ratio of 2 to carbonyl-reduction
products, as well as the formation of minor
unidentified degradation products.
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ACKNOWLEDGMENTS
The California Institute of Technology Center for Catalysis and
Chemical Synthesis is gratefully acknowledged for access to
analytical equipment. We thank S. Virgil and J. Hofstra for
assistance in obtaining x-ray–quality crystals and solving the
structure of 15, respectively. M. Takase and L. Henling are
acknowledged for acquiring the x-ray diffraction data for
15 (CCDC deposition no. 1478621; the data are available free of
charge from The Cambridge Crystallographic Data Centre).
M. Kieffer is gratefully acknowledged for critical feedback and
helpful suggestions. Fellowship support was provided by the
National Science Foundation (graduate research fellowship to
K.V.C., grant DGE-1144469) and the Shenzhen UV-ChemTech Inc.
(postdoctoral fellowship to C.X.). S.E.R. is an American Cancer
Society Research Scholar and Heritage Medical Research
Institute investigator. Financial support from the NIH (National
Institute of General Medical Sciences grant RGM097582-01),
Eli Lilly, and Novartis is gratefully acknowledged. The California
Institute of Technology has filed a provisional patent on
this work (application no. 62/269,760).
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SUPPLEMENTARY MATERIALS
www.sciencemag.org/content/353/6302/912/suppl/DC1
Materials and Methods
Schemes S1 and S2
Tables S1 to S9
References (46–53)
NMR Spectra
9 May 2016; accepted 25 July 2016
10.1126/science.aag1028
SCIENCE sciencemag.org
26 AUGUST 2016 • VOL 353 ISSUE 6302 915

A 15-step synthesis of (+)-ryanodol
Kangway V. Chuang, Chen Xu and Sarah E. Reisman (August 25,
2016)
Science 353 (6302), 912-915. [doi: 10.1126/science.aag1028]
Editor's Summary
Rapid ryanodol route
The plant-derived compound ryanodine and its hydrolyzed cousin ryanodol are biochemically
interesting for their calcium-regulating capacity and chemically interesting for their dense tangle of
carbon rings brimming with oxygen appendages. Chuang et al. report an efficient 15-step asymmetric
synthesis of ryanodol from the structurally much simpler terpene pulegone (see the Perspective by
Verdaguer). Key steps include a Pauson-Khand cyclization of a tethered alkene and alkyne with carbon
monoxide to set the ring motifs, followed by an oxidation using selenium dioxide that delivers three
different oxygen substituents in tandem.
Science, this issue p. 912; see also p. 866
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